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Research Paper
Combined garnet, scheelite and apatite U–Pb dating of mineralizing
events in the Qiaomaishan Cu–W skarn deposit, eastern China
Yue Li
a,b,c
, Feng Yuan
a,b,
⇑
, Simon M. Jowitt
c
, Xiangling Li
a,b
, Taofa Zhou
a,b
, Fangyue Wang
a,b
,
Yufeng Deng
a,b
a
Ore Deposit and Exploration Centre (ODEC), Hefei University of Technology, Hefei 23009, China
b
Anhui Province Engineering Research Center for Mineral Resources and Mine Environments, Hefei 23009, China
c
Department of Geoscience, University of Nevada Las Vegas, 4505 S. Maryland Pkwy., NV 89154-4010, USA
article info
Article history:
Received 1 March 2022
Revised 1 August 2022
Accepted 18 August 2022
Available online 27 August 2022
Handling Editor: N.M.W. Roberts
Keywords:
In-situ scheelite U–Pb dating
In-situ garnet U–Pb dating
In-situ apatite U–Pb dating
Qiaomaishan skarn deposit
abstract
Determining the precise timing of mineralization and mineralizing events is crucial to understanding
regional mineralizing and other geological events and processes. However, there are a number of miner-
alogical and analytical limitations to the approaches developed for the absolute dating of mineralizing
systems, such as molybdenite Re–Os and zircon and garnet U–Pb, among others. This means that the pre-
cise and accurate dating of mineralizing systems that may not contain minerals suitable for dating using
existing approaches requires the development of new (and ideally in situ) approaches to absolute dating.
This study outlines a new in situ analytical approach that has the potential to rapidly and accurately eval-
uate the timing of ore formation. Our study employs a novel application of in situ scheelite U–Pb dating
analysis using laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) and samples
from the Qiaomaishan deposit, a representative example of skarn mineralization within the Xuancheng
ore district of eastern China. Our approach to scheelite dating of the deposit is verified by cross-
comparison to dating of cogenetic garnet and apatite, proving the effectiveness of this approach. Our
new approach to dating of scheelite-bearing geological systems is rapid, cheap, requires little sample
preparation, and is undertaken in situ, allowing crucial geological and mineralogical context to be
retained during analysis. The approaches outlined here not only allow the determination of the absolute
timing of formation of the Qiaomaishan deposit through the U–Pb dating of scheelite [138.6 ± 3.2 Ma,
N= 39, mean square weighted deviation (MSWD) = 1.17], garnet (138.4 ± 1.0 Ma, N= 40,
MSWD = 1.3), and apatite (139.6 ± 3.3 Ma, N= 35, MSWD = 0.72), but also further supports the theoretical
genetic links between this mineralization and the emplacement of a proximal porphyritic granodiorite
intrusion (zircon U–Pb age: 139.5 ± 1.2 Ma, N= 23, MSWD = 0.3). Moreover, our research indicates that
the higher the concentrations of U within scheelite, the more suitable that scheelite is for U–Pb dating,
with the main factor controlling the U content of scheelite seemingly being variations in oxygen fugacity
conditions. This novel approach provides a potentially powerful tool, not just for the dating of skarn sys-
tems but also with potential applications in orogenic and intrusion-related gold, porphyry W–Mo, and
greisen mineralizing systems as well as other scheelite-bearing geological bodies or geological systems.
Ó2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by
Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
licenses/by-nc-nd/4.0/).
1. Introduction
Multiple isotopic dating approaches have been used to deter-
mine the timing of mineralizing events, including molybdenite
Re–Os and the dating of hydrothermal minerals (e.g., garnet, titan-
ite, cassiterite, etc.) using U–Pb approaches (e.g., Zhang et al.,
2017, 2019; Gevedon et al., 2018; Xie et al., 2019; Alexander et al.,
2020; Xiao et al., 2020; Hong et al., 2021; Li et al., 2021b). However,
a lack of suitable minerals (especially ore minerals) for dating makes
determining the processes involved in the timing of mineralization
and alteration events within skarn or other hydrothermal systems
often controversial. Several possible approaches for the in-situ U–
Pb isotopic dating of hydrothermal minerals within skarn systems
(e.g., garnet, apatite, etc.) have been recently outlined, the majority
of which use laser ablation–inductively coupled plasma–mass spec-
trometry (LA–ICP–MS; Deng et al., 2017; Seman et al., 2017).
Despite these advances there remain numerous limitations in terms
https://doi.org/10.1016/j.gsf.2022.101459
1674-9871/Ó2022 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
⇑
Corresponding author.
E-mail address: yf_hfut@163.com (F. Yuan).
Geoscience Frontiers 14 (2023) 101459
Contents lists available at ScienceDirect
Geoscience Frontiers
journal homepage: www.elsevier.com/locate/gsf
of obtaining precise dates for skarn mineralization as well as for
other mineral deposit types, including the fact that not all of the
minerals dateable using current approaches are present in most
deposits. In addition, a number of potential approaches require min-
eral separation rather than in situ analysis, with the potential loss of
the mineralogical and geological context of the minerals being
dated. This indicates the requirement for the new development of
in situ U–Pb and other geochronological approaches for the deter-
mining of the precise timing of mineralizing and other events within
hydrothermal, mineralizing, and other geological systems.
Scheelite commonly occurs in skarn-type, vein/stockwork, por-
phyry deposits, disseminated or greisen, orogenic and intrusion-
related gold, and breccia and brine/evaporite and hot spring depos-
its, among others (Brown and Pitfield, 2014). The widespread dis-
tribution of scheelite within these diverse mineralizing systems
means that the development of approaches to date this mineral
will have broad applicability. The Qiaomaishan deposit is a rela-
tively simple skarn system within the Xuancheng ore district of
the Middle–Lower Yangtze River Metallogenetic Belt (MLYB), east-
ern China. Previous research (Li et al., 2019, 2021b) indicates that
the formation of this deposit and the associated skarn alteration
is related to the intrusion of a porphyritic granodiorite. This
deposit does not involve multi-stage magmatic and/or thermal
events (Li et al., 2019, 2021a), which makes the deposit an ideal
case study for the application of scheelite U–Pb dating, especially
as this approach can be directly compared to dates obtained using
other approaches on the same deposit. This study focuses on the
hydrothermal garnet, scheelite, and apatite from the Qiaomaishan
deposit, with the multiple approaches to dating of the system
allowing the determination of whether accurate, precise, and more
importantly geologically meaningful ages can be obtained from
scheelite.
Previous research has highlighted the use of scheelite Sm–Nd
dating to determine the timing of mineral deposit formation, an
approach that can yielded geologically significant ages (Peng
et al., 2003; Liu et al., 2007), albeit with low precision (Stein,
2014). However, relatively few studies have been undertaken on
the in situ dating of scheelite, namely Wintzer (2019), Poitrenaud
et al. (2020) and a conference abstract by Raith et al. (2011). The
first two studies undertook the in-situ U–Pb dating of scheelite
using NIST glasses as reference materials as a result of a lack of
scheelite standards. However, the presence of significant matrix
effects between NIST612 and scheelite (Tang et al., 2022) means
that these initial attempts at dating are likely not very accurate
(Poitrenaud et al., 2020). In addition, the space limitations of the
conference abstract means that Raith et al. (2011) did not provide
details of the analytical methods, reference materials, the instru-
ment parameters used, the results obtained and their accuracy
and precision, and key illustrations such as Tera-Wasserburg dia-
grams (Tera and Wasserburg, 1972). This means that it is impossi-
ble to tell whether this scheelite dating was successful or not and
whether this approach could be applied to other deposits. All of
this indicates that significant uncertainty remains over the use
and applicability of scheelite U–Pb dating as a means to obtain
absolute dates for mineralizing events and other geological pro-
cesses. This study provides details of the analytical methods and
instrument parameters as well as geological background informa-
tion in addition to comparing scheelite ages to the U–Pb dating of
garnet and apatite from the same deposit, allowing the verification
of the precision and accuracy of this widely applicable approach to
scheelite U–Pb dating.
2. Geological setting
2.1. Regional geology
The Middle–Lower Yangtze River Metallogenetic Belt (MLYB)
hosts world-class Cu–Fe polymetallic mineralization and is one of
Fig. 1. Geological map of the Middle–Lower Yangtze River Metallogenic Belt showing the location of major ore districts and the study area (modified after Chang et al., 1991;
Mao et al., 2011; Zhou et al., 2017).
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
2
the most important areas of mineralization in China (Fig. 1;Chang
et al., 1991; Mao et al., 2011; Pirajno and Zhou, 2015; Zhou et al.,
2017). The belt is subdivided into southern, central, and northern
subzones (Fig. 1) and is bounded by the Xiangfan–Guangji Fault
(XGF) to the northwest, the Huanglishu–Poliangting Fault (HPF)
to the northeast and the Chongyang–Changzhou Fault (CCF) to
the south (Fig. 1;Zhou et al., 2017). The ore deposits within this
belt are concentrated in eight districts, with the Xuancheng district
being relatively newly discovered and hence under-explored
relative to the other districts within the belt. The region hosts a
number of Cu–polymetallic deposits that are related to Early
Cretaceous intrusions (Fig. 2;Liu and Duan, 2015; Li et al., 2020).
The Qiaomaishan (QMS) deposit is a representative skarn
deposit in Xuancheng district and forms the focus of this study
(Figs. 2–3).
2.2. Ore deposit geology
The Qiaomaishan deposit is located to the northeast of Xuan-
cheng (Fig. 2A) and is a medium-sized skarn-type deposit with
total estimated resources of 60,000 t of Cu metal at an average
grade of 1.03% and 10,000 t of W at an average grade of 0.25%
WO
3
(Liu and Duan, 2015). The main stratigraphic units in this area
include upper Devonian, middle–upper Carboniferous, upper Per-
mian, and Quaternary sediments (Fig. 3A). The upper Devonian
sediments in this region are quartz sandstones whereas the Car-
boniferous sediments are dominated by limestones with a basal
section containing dolomitic limestones. The majority of this lime-
stone has been contact metamorphosed to form medium- to
coarse-grained marble and garnet skarn, with all of the economic
skarn-type orebodies also located within these metasomatized
zones (Fig. 3;Liu and Duan, 2015). The upper Permian sediments
in this area are quartz sandstones that are in contact with the
lower parts of the intrusions within this region although this con-
tact relationship is typically free of any hydrothermal alteration.
The main geological structure within the study area is an over-
turned anticline with a core that consists of Devonian sandstone
units (Liu and Duan, 2015). The mineralization-related intrusion
in this area is a porphyritic granodiorite that yielded a zircon U–
Pb age of 139.5 ± 1.2 Ma [N= 23, mean square weighted deviation
(MSWD) = 0.3, by LA–ICP–MS; Li et al., 2019]. This intrusion is the
product of emplacement after mixing of enriched mantle-derived
and crust-derived magmas (Li et al., 2019) and is present in the
form of stocks or dikes that were emplaced into the surrounding
Carboniferous limestone units (Liu and Duan, 2015). The contact
zone between the intrusions and this limestone is an important
host for the skarn Cu–W mineralization in this area (Fig. 3). Both
mineralization and the intrusion are located on the lower limb of
the anticline and are covered by the other limb.
Field, geological and petrographic observations allow the deter-
mination of a paragenetic sequence and associated ore-forming
processes that can be divided into four main stages as follows:
(1) prograde skarn, (2) retrograde, (3) main sulfide mineralization,
and (4) quartz–carbonate stages (Fig. 4). These stages are described
below.
2.2.1. Prograde skarn stage (stage 1)
This stage represents the prograde skarn formation associated
with the generation of anhydrous silicate minerals, namely abun-
dant garnet skarn and lesser amounts of vein-hosted diopside
Fig. 2. Map showing the geology of the Xuancheng ore district (modified after Liu and Duan, 2015; Li et al., 2020, 2021a, 2021b).
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
3
(Fig. 5). This alteration is predominantly located within the por-
phyritic granodiorite (Fig. 5A–D) and is associated with the forma-
tion of pink–brown endoskarn garnet and red–brown or green
exoskarn garnet that overprint and replace the altered porphyritic
granodiorite and the surrounding Carboniferous units (Fig. 5),
respectively. The pink–brown and red–brown type of garnet
formed proximal to the contact between the intrusion and the sur-
rounding country rock (Fig. 5B–E) whereas the green type garnet is
more widely distributed (Fig. 5G), being identified distal from the
contact zone throughout the deposit. Cross-cutting relationships
within the deposit indicate that the green exoskarn garnet formed
after the red–brown exoskarn garnet (Fig. 5F; Li et al., 2021a).
2.2.2. Retrograde stage (stage 2)
This stage is associated with retrograde skarn alteration and the
formation of hydrous silicate minerals such as epidote, antigorite,
and chlorite, as well as garnet, magnetite, scheelite, quartz, and
apatite (Fig. 6). It is associated with exoskarn formation through-
out the deposit, and includes an alteration zone dominated by
antigorite that formed proximal to the contact zone (Fig. 6A–C),
Fig. 3. Geological map (A–C) and cross-sections (D–F) showing the location of the mineralization-related intrusion and skarn zones in the study area as well as the orebodies
that define the Qiaomaishan deposit (modified after Liu and Duan, 2015; Li et al., 2021b).
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
4
reflecting the presence of dolomitic limestone. This antigorite
alteration zone is free of sulfides but contains a small amount of
magnetite. The antigorite zone also transitions into an andradite
garnet-dominated skarn with increasing distance from the contact
before again transitioning into small garnet-hosted veins within
marble units distal from the intrusion (Fig. 6D–F). Epidote is com-
paratively rare and is only developed in epidote-dominated
patches that contain small amounts of magnetite and quartz
(Fig. 6G). This stage is also associated with the pseudomorphic
replacement of earlier-formed garnet by magnetite, chlorite and
sericite (Fig. 6H–I), providing evidence of the overprinting of pro-
grade skarn by retrograde alteration.
2.2.3. Main sulfide mineralization stage (stage 3)
This stage represents the main stage of sulfide mineralization
and involved the precipitation of sulfides and quartz. The sulfides
formed during this stage of mineralization include pyrite, chal-
copyrite, molybdenite, and pyrrhotite, all of which are hosted by
massive sulfide ores and quartz–sulfide veins that cross-cut the
earlier-formed skarn assemblages (Fig. 7A–B). This stage of miner-
alization is also characterized by the formation of quartz–molyb-
denite veins that cross-cut the altered intrusion (Fig. 7C). The
main orebodies within the deposit formed during this stage and
consist of massive sulfides with minor amounts of gangue
(Fig. 7D). This stage is also associated with continued scheelite
Fig. 4. The paragenetic sequence of mineralization and alteration recorded within the Qiaomaishan deposit showing the mineralogical variations between the four stages of
mineralization identified in the study area.
Fig. 5. Photographs showing representative samples of (A) altered porphyritic granodiorite, (B–D) endoskarn, and (E) exoskarn within the Qiaomaishan deposit.
Abbreviations are as follows: Di = diopside, Grt = garnet.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
5
precipitation, as evidenced by the relationship between scheelite
and massive sulfides (Fig. 7E). Intimate contact relationships
between scheelite and chalcopyrite also indicates that the majority
of the scheelite in the deposit formed during this stage of mineral-
ization (Fig. 7F).
2.2.4. Quartz–carbonate stage (stage 4)
The final stage of mineralization, here termed the quartz–
carbonate stage, generated quartz–carbonate veins that contain
pyrite, chalcopyrite, and galena (Fig. 8). This stage contrasts with
the main mineralization stage in that it is associated with a
Fig. 6. Photographs and photomicrographs showing representative examples of the retrograde skarn stage of mineralization within the Qiaomaishan deposit. (A–C) Hand
specimens and photomicrographs of antigorite skarn with (B) and (C) taken under transmitted plane-polarized and transmitted cross-polarized light, respectively. (D–F)
Hand specimens and photomicrographs of garnet exoskarn and garnet veins within marble; (E) was taken under transmitted plane-polarized light. (G) Hand specimen of
epidote skarn. (H, I) Garnet pseudo-crystalline and replaced by magnetite and chlorite, respectively; (H) and (I) were taken under transmitted plane-polarized and
transmitted cross-polarized light, respectively. Abbreviations are as in Fig. 5 with Atg = antigorite, Ep = epidote, Mt = magnetite, Chl = chlorite, Sch = scheelite, Ser = sericite,
Cal = calcite.
Fig. 7. Photographs and photomicrographs showing representative samples formed during the main mineralization stage and cross-cutting relationships within the
Qiaomaishan deposit. (A–C) Hand specimen containing quartz–sulfide veins cross-cutting earlier formed garnet skarn and porphyritic granodiorite. (D–F) Hand specimens
and photomicrographs showing a representative example of massive sulfide ore and (E) showing that the paragenesis of scheelite with sulfide; (E) was taken under ultraviolet
light whereas (F) was taken under reflected light. Abbreviations are as in Fig. 6 with Qtz = quartz, Ccp = chalcopyrite, Mo = molybdenite, Py = pyrite.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
6
quartz–calcite or pure calcite gangue assemblage (Fig. 8A–D). The
sulfide assemblage formed during this stage is pyrite dominated
with minimal amounts of chalcopyrite, indicating that this stage
of mineralization is not economically important. This stage of
mineralization is also more distal from the contact zone than
the main stage of mineralization. The later parts of this stage
(i.e., after sulfide precipitation) are associated with the formation
of pure calcite veins free of sulfides that cross-cut the earlier-
formed mineralization and the antigorite alteration zone
(Fig. 8E–H). There are also some gypsum veins formed during this
stage of mineralization and cross-cut the earlier formed antigorite
alteration assemblages (Fig. 8I), garnet skarn assemblages (Fig. 8J),
and sulfide veins (Fig. 8K), suggesting that the gypsum formed
during the very final stages of hydrothermal activity. Pure calcite
veins are generally located in areas distal from the contact zone
whereas the gypsum veins are predominantly located within the
antigorite alteration zone. This means that although the relative
timing of the pure calcite and gypsum veins cannot be determined
and both formed during the final stage of the hydrothermal activ-
ity in this area.
3. Samples
3.1. Scheelite samples
The scheelite mineralization in the deposit formed during
stages 2 and 3 and can be divided into three types according to par-
agenetic and spatial relationships. Type 1 (sample QMS-16–02;
Fig. 3D) scheelite is located proximal (within 30 m) to the contact
between the intrusion and the surrounding limestone country rock
and is fine-grained. It usually forms part of a garnet–quartz–schee
lite–magnetite alteration assemblage (Fig. 9A–E). Type 2 scheelite
(QMS-18–02; Fig. 3F) is found more distal from the contact zone
(60 m) but again is fine-grained and is associated with an
antigorite–phlogopite–scheelite–magnetite alteration assemblage
(Fig. 9F–J). Type 3 scheelite (QMS-29) is spatially related to the
main orebodies and is the scheelite that was dated using the U–
Pb technique during this study. This scheelite is coarser grained
than the Type 1 and 2 scheelite (up to 2 mm or more) and is asso-
ciated with a scheelite–apatite–dolomite–chalcopyrite–pyrite–cal
cite alteration assemblage (Fig. 10).
Fig. 8. Photographs and photomicrographs showing representative examples of the quartz–carbonate stage and cross-cutting relationships within the Qiaomaishan deposit.
(A–D) Photomicrographs showing the quartz–calcite–sulfide assemblages; (B) and (C) were taken under transmitted cross-polarized light whereas (D) was taken under
reflected light. (E–H) Photographs and photomicrographs showing the stage 4 pure calcite veins cross-cutting earlier formed alteration and mineralization, (F), (G), and (H)
were taken under transmitted cross-polarized light, reflected light and transmitted plane-polarized light, respectively. (I–K) Gypsum veins cross-cutting earlier formed
antigorite alteration zone, garnet skarn, and early (Stage 3) sulfide veins. Abbreviations are as in Figs. 5–7 with Gn = galena.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
7
3.2. Samples for U–Pb dating
Garnet was collected from drillhole 16 + 02 at a depth of –108 m
(QMS-16–21; Fig. 11). This sample is a massive garnet skarn con-
taining garnet that is generally 5–10 mm in size along with minor
disseminated magnetite and pyrite (Fig. 11A). The sample was col-
lected from exoskarn that is located spatially close to the contact
zone and formed during stage 1, later than the endoskarn garnet
and earlier than the green exoskarn garnet (Fig. 11A; Li et al.,
2021b). A polished thin section was prepared from this sample
for optical microscopy, with the mostly reddish–brown garnet in
hand specimen appearing as a light yellowish–brown color under
transmitted plane-polarized light (Fig. 11B). The garnets are euhe-
dral and are free of fractures and alteration, indicating that they
underwent little interaction with later hydrothermal fluids. They
also have generally homogenous major element compositions, as
evidenced by their uniform appearance during backscattered elec-
tron (BSE) imaging (Fig. 11C; Li et al., 2021a). Disseminated pyrite–
chalcopyrite mineralization also fills the interstitial spaces
between the garnets in this sample (Fig. 11D, E). This suggests that
these sulfides formed after the formation of garnet skarn but that
this mineralization did not lead to any alteration of the garnet.
The Type 3 scheelite and apatite dated during this study are
both from the same hand specimen that was collected from
underground developments within the study area. The sample
contains high concentrations of Cu and W and a large amount
of chalcopyrite and disseminated pyrite along with gangue miner-
als (Fig. 10A, B). Early scheelite–apatite–chalcopyrite–dolomite
alteration assemblages are cross-cut by later pyrite veins within
the sample (Fig. 10C). The textures between the scheelite, apatite,
and chalcopyrite in this sample indicates they formed almost
simultaneously (Fig. 10D–J). The paragenesis of the scheelite
and the sulfides within the deposit also suggests that the scheel-
ite formed during the early parts of the sulfide stage of
mineralization.
4. Analytical methods
Polished thin sections were prepared from representative hand
specimens containing scheelite formed during the different stages
of mineralization outlined above. The optical microscopy and geo-
chemical data for scheelite presented in this study are based on
observations and analyses of these thin sections.
Fig. 9. Photographs and photomicrographs showing representative examples of the Type 1 (A–E) and Type 2 (F–J) scheelite within the Qiaomaishan deposit. (B, D, G, I) were
taken under transmitted plane-polarized light and (C, E, H, J) were taken under transmitted cross-polarized light. Abbreviations are as Figs. 5–7 with Phl = phlogopite.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
8
4.1. Major and trace element composition of scheelite
Scheelite compositions were determined by electron probe
microanalysis (EPMA) employing a JOEL JXA 8230 electron micro-
probe equipped with wave and energy dispersive detectors and a
backscattered electron detector at the School of Resources and
Environmental Engineering, Hefei University of Technology, Hefei,
China. This instrument was also used for BSE imaging. The EPMA
Fig. 10. Photographs and photomicrographs showing representative examples of the Type 3 scheelite within the Qiaomaishan deposit. (C, D, G) were taken under reflected
plane-polarized light, (E, I) were taken under transmitted plane-polarized light, and (F, H, J) were taken under transmitted cross-polarized light. Abbreviations are as in
Figs. 6–7 with Ap = apatite, Dol = dolomite.
Fig. 11. Photographs, photomicrographs, and a BSE image (C) showing representative examples of the QMS-16–21 garnet skarn within the Qiaomaishan deposit. (B, E) were
taken under transmitted plane-polarized light and (D) was taken under reflected plane-polarized light. Abbreviations are as in Figs. 5–7.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
9
undertaken during this study used an accelerating voltage of 15 kV,
a beam current of 20 nA, an electron beam diameter of 3
l
m, and a
counting time of 20 s. Natural and synthetic minerals were used as
standards and a standard ZAF program was employed for matrix
corrections. The analytical precision of the concentrations of the
majority of elements determined during this analysis is better than
1%.
Scheelite LA–ICP–MS trace element analysis was undertaken at
the In-situ Mineral Geochemistry Lab, Ore Deposit and Exploration
Centre (ODEC), Hefei University of Technology, Hefei, China,
using an Agilent 7900 Quadrupole ICP–MS coupled to a Photon
Machines Analyte HE 193-nm ArF Excimer LA system. Argon was
used as a make-up gas and was mixed with the carrier gas via a
T-connector before entering the ICP (Ning et al., 2017; Wang
et al., 2017). Trace element concentrations were determined using
a uniform spot size diameter of 40
l
m at 8 Hz with a laser energy
of 4 J/cm
2
and an ablation period of 40 s after 20 s of gas blank
measurement. Standard reference materials NIST 610, NIST 612,
and BCR-2G were used for external standardization with preferred
elemental concentrations for these NIST and USGS reference
glasses taken from the GeoReM database (Jochum et al., 2005).
These standard reference materials were run after every 10
unknowns with detection limits calculated for each individual ele-
ment in each individual spot analysis. Offline data processing was
performed using the ICPMSDataCal software (Liu et al., 2008).
4.2. In-situ U–Pb dating
U–Pb dating of garnet, apatite, and scheelite was undertaken on
regular polished thin sections. In-situ U–Pb geochronology was
undertaken using LA–ICP–MS at the Yanduzhongshi Geological
Analysis Laboratories Limited, Beijing, China. The instrumental
conditions are reported in Supplementary Data (Table S1). All ref-
erence materials were analyzed at the beginning of the session and
after every 10 unknown spots using the same conditions as used on
the samples and each analysis began with a 20 s blank gas mea-
surement followed by a further 40 s of analysis time when the laser
was switched on. A flow of He carrier gas at a rate of 0.6 L/min car-
ried particles ablated by the laser out of the chamber to be mixed
with Ar gas and then carried to the plasma torch. Off-line data pro-
cessing was completed using the ZSkits and ICPMSDataCal soft-
ware packages (Liu et al., 2008, 2010; Cai et al., 2020), and
results are plotted in Tera–Wasserburg diagrams using Isoplot ver-
sion 4.15 (Ludwig, 2012). Uncertainty propagation and data report-
ing follow the community-based guidelines of Horstwood et al.
(2016), Roberts et al. (2020), and Sliwinski et al. (2022).
For garnet dating, a MALI grandite garnet standard (Seman
et al., 2017) was used as the primary standard with a Willsboro
andradite standard garnet (Seman et al., 2017) and an in-house
ZSLS garnet reference material (reference age of 155 ± 2 Ma deter-
mined by LA–ICP–MS age) used as monitors. This analysis used a
55
l
m laser diameter, a frequency of 9 Hz, and an energy density
of approximately 3 J/cm
2
.
For apatite dating, a MAD2 apatite was used as the primary ref-
erence material (Thomson et al., 2012), with Otter Lake (Barfod
et al., 2005; Chew et al., 2011) and ZAP-10 [in-house reference
material, reference age of 155 ± 2 Ma determined by LA–ICP–MS;
also named MRC-1 with an isotope dilution–thermal ionization
mass spectrometry (ID-TIMS) age of 153.3 ± 0.2 Ma, Apen et al.,
2022] apatite used as monitor standards. Apatite analyses used a
50
l
m diameter laser beam, a frequency of 8 Hz, and an energy
density of approximately 3.6 J/cm
2
.
For scheelite dating, it should be noted that there are currently
no published reference materials that can be used for calibration,
mass discrimination, and isotope fractionation. As a result, matrix
effects were avoided by the use of an in-house laboratory scheelite
reference material ZS-Sch-1 (reference age of 228 ± 2 Ma deter-
mined by ID-TIMS; Dr. Han Zhang, pers. comm., the Yanduzhongshi
Geological Analysis Laboratories Ltd.) for calibration, mass discrim-
ination, and isotope fractionation in this study. Since the details of
this reference material have not been officially published, we can
only assess whether the results of scheelite are credible by com-
paring with the dating results of apatite coexisting with scheelite
under the assumption that the reference material is accurate and
reliable; preparation of a publication outlining the details of this
reference material is currently underway. The precision of the data
obtained during this study also meant that it was not possible to
identify the absolute timing of the different potential stages of
hydrothermal events in the study area by LA–ICP–MS U–Pb dating.
However, the results of the garnet and apatite dating undertaken
during this study can be used to determine whether our scheelite
U–Pb dating results are credible and geologically meaningful, indi-
cating the usefulness of combined garnet–apatite–scheelite dating
of the deposit. Scheelite also contains more U than the apatite anal-
ysed during this study, meaning that a 45
l
m laser beam was used
with all other conditions for scheelite dating similar to those used
for apatite.
5. Results
5.1. Scheelite major and trace element geochemistry
The results of the EPMA and the LA–ICP–MS analysis under-
taken during this study are given in Supplementary Data (Tables
S2 and S3). Type 1 scheelite contains relatively uniform concentra-
tions of CaO (19.71–20.72 wt.%, average = 20.22 wt.%; N= 15) along
with the lowest concentrations of WO
3
(73.19–78.71 wt.%,
average = 75.95 wt.%; N= 15) but the highest concentrations of
MoO
3
(0.92–5.73 wt.%, average = 3.32 wt.%; N= 15; data from
EPMA) of any of the scheelite formed during the three different
types identified above. Type 2 scheelite contains similar concentra-
tions of CaO to the Type 1 scheelite (19.61–20.38 wt.%, average =
19.79 wt.%; N= 11) but more WO
3
(75.70–81.26 wt.%, average =
79.67 wt.%; N= 11; data from EPMA) and significantly less MoO
3
(0.06–0.46 wt.%, average = 0.15 wt.%; N= 11) than the Type 1
scheelite. The Type 3 scheelite has CaO concentrations (19.38–
20.01 wt.%, average = 19.79 wt.%; N= 22) that are similar to the
concentrations within the scheelite formed during the other two
types but contains slightly more WO
3
(77.90–80.74 wt.%,
average = 80.04 wt.%; N= 22), and significantly less MoO
3
(0–
0.15 wt.%, average = 0.05 wt.%; N= 22; data from EPMA), including
seven analyses where MoO
3
concentrations were below detection.
Type 1 scheelite also has low total rare earth element (REE) con-
centrations (25.33–52.89 ppm; N= 13; Supplementary Data,
Table S3) and contains low concentrations of U (0–18.99 ppm,
average = 2.01 ppm; N= 13; Supplementary Data,Table S3) but
high concentrations of Mo (4439–29,923 ppm, average = 17,121 p
pm; N= 13; data from LA–ICP–MS; Supplementary Data,Table S3).
This scheelite is also light REE (LREE) enriched and heavy REE
(HREE) depleted with variable Eu anomalies
ðEu=Eu;Eu=Eu
¼
Eu
sample
=Eu
chondrite
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Sm
sample
=Sm
chondrite
ðÞ
Gd
sample
=Gd
chondrite
ðÞ
pÞvisible in
chondrite-normalized REE diagrams (0.38–4.41; N= 13;
Fig. 11A). The Type 2 scheelite contains higher concentrations of
the total REE (92.15–211.37 ppm; Supplementary Data,Table S3),
and U (0.42–20.01 ppm, average = 4.21 ppm; N= 13; Supplemen-
tary Data,Table S3) but lower concentrations of Mo (265–
1699 ppm, average = 752 ppm; N= 13; data from LA–ICP–MS; Sup-
plementary Data,Table S3) than the Type 1 scheelite. The Type 2
scheelite also has relatively flat chondrite-normalized REE patterns
with significantly positive Eu anomalies (1.95–5.93; Fig. 12B). The
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
10
Type 3 scheelite contains the highest concentrations of the REE
(277.88–1483.97 ppm; N= 15; Supplementary Data,Table S3)
and U (1.32–67.72 ppm, average = 36.28 ppm; N= 15; Supplemen-
tary Data,Table S3) but also the lowest concentrations of Mo
(11.98–27.62 ppm, average = 16.86 ppm; N= 15; data from LA–
ICP–MS; Supplementary Data,Table S3) of the scheelite analyzed
during this study. This scheelite has chondrite-normalized REE pat-
terns that are similar to the Type 2 scheelite but with even more
pronounced positive Eu anomalies (9.78–398.69; Fig. 7C).
5.2. In-situ dating results
Variations in mineral structure mean that some minerals used
for U–Pb dating, such as apatite, garnet, scheelite, and others, will
incorporate a certain amount of common Pb in their mineral lat-
tices during formation. A common Pb correction has not been
applied in this study as a result of the high variability of the data
(Chew et al., 2014; Reinhardt et al., 2022). This also means that
U–Pb ages are calculated using a linear regression within Tera–
Wasserburg concordia diagrams (Tera and Wasserburg, 1972)as
the garnet, apatite, and scheelite all incorporate a mixture of
non-radiogenic and radiogenic Pb formed as a result of the in-
situ decay of U. All U–Pb dates are defined as the lower intercept
with the concordia curve as determined by linear regression of dis-
cordant arrays with reported ages calculated using Isoplot 4.15
(Ludwig, 2012) with all uncertainties reported at the 2
r
level.
The resulting U–Pb isotopic data and the Tera–Wasserburg dia-
grams for the samples and reference materials used during this
study are given in Supplementary Data (Table S4) with garnet, apa-
tite, and scheelite U–Pb isotopic data shown in Fig. 13 and Tera–
Wasserburg diagrams of these reference materials provided in
Supplementary Data (Fig. S1). The U–Pb isotopic data for the garnet
from sample QMS-16–21 plotted on a Tera–Wasserburg diagram
define a regression line that yields a well-defined lower-intercept
age of 138.4 ± 1.0 Ma (2
r
,N= 40, MSWD = 1.3; Fig. 13A). The U–
Pb ages for apatite and scheelite from sample QMS-29 determined
using lower intercepts are identical within uncertainty at 139.6 ± 3.
3Ma(2
r
,N= 35, MSWD = 0.71; Fig. 13B) and 138.6 ± 3.2 Ma (2
r
,
N= 39, MSWD = 1.17; Fig. 13C), respectively.
6. Discussion
6.1. Hydrothermal fluid processes and the incorporation of U into the
scheelite structure
The major, trace, and REE concentrations of scheelite are influ-
enced by numerous factors that include hydrothermal fluid com-
positions, oxygen fugacity (fO
2
), and host rock buffering (Brugger
et al., 2000; Dostal et al., 2009; Song et al., 2014; Guo et al.,
2016; Fu et al., 2021). This in turn means that variations in
scheelite geochemistry can be used to identify key changes
during the evolution of mineralizing hydrothermal systems. The
scheelite within the study area contains significantly different
Fig. 12. (A–C) Chondrite-normalized REE patterns for scheelite formed during different types of mineralization within the Qiaomaishan deposit normalized to the C1
chondrite composition of McDonough and Sun (1995). These diagrams also show the composition of the endoskarn garnet (Li et al., 2021a) in the study area. (A) Chondrite-
normalized REE patterns for Type 1 scheelite and exoskarn garnet (Li et al., 2021a). (B) Comparison of Type 1 and Type 2 scheelite. (C) Comparison of Type 1, Type 2, and Type
3 scheelite. (D) Diagram showing variations in WO
3
and MoO
3
concentrations within scheelite in the study area. Linear equations and correlation coefficients refer to the solid
trendlines defined by the Type 1 scheelite data.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
11
concentrations of MoO
3
as outlined above (Supplementary Data,
Table S2). Molybdenum is a redox-sensitive element that is trans-
ported as Mo
6+
and enters scheelite by substituting for W
6+
under
oxidizing conditions. A reduction in fO
2
conditions would cause
Mo
6+
to be reduced to Mo
4+
and hence precipitate as molybdenite
(MoS
2
;Rempel et al., 2009; Song et al., 2014). This means that
scheelite containing higher concentrations of Mo formed under
oxidizing conditions whereas scheelite containing lower concen-
trations of Mo formed in a more reduced environment (Zhao
et al., 2018). The three types of scheelite formation identified
within the Qiaomaishan deposit are associated with scheelite Mo
concentrations that decrease over time, as evidenced by both
EPMA and LA–ICP–MS analyses (Supplementary Data, Tables S2
and S3;Fig. 12D). Type 1 scheelite contains the highest concentra-
tions of Mo and has WO
3
and MoO
3
concentrations that negatively
correlate (R
2
= 0.83; Fig. 12D), consistent with the substitution
mechanism outlined above. However, the Types 2 and 3 scheelites
contain low concentrations of Mo and have WO
3
and MoO
3
con-
centrations that do not correlate (Fig. 12D). This suggests these
later scheelites formed under lower oxygen fugacity (or reduced)
conditions associated with very low Mo
6+
/Mo
4+
ratios, allowing
only limited isomorphic substitution between W and Mo (Fu
et al., 2021). This means that the differences in scheelite Mo con-
centrations between Types 1 and 3 reflect a decrease in fO
2
condi-
tions during the evolution of the mineralizing systems. All three of
the scheelite samples analyzed during this study are located within
the exoskarn part of the deposit, indicating that the variations in
Mo concentrations within these samples cannot be related to host
rock buffering, again supporting a hydrothermal fluid oxygen
fugacity control on the Mo concentrations of these scheelite
samples.
The REE concentrations within scheelite can also be influenced
by various other factors (Ghaderi et al., 1999; Dostal et al., 2009;
Song et al., 2014). There are three main processes whereby the
trivalent REE can substitute for the divalent Ca within the scheelite
structure, namely: (1) 2Ca
2+
= REE
3+
+Na
+
, (2) Ca
2+
+W
6+
= REE
3+
+
Nb
5+
, or (3) 3Ca
2+
= 2REE
3+
+Ca
vacancy
(Ghaderi et al., 1999; Brugger
et al., 2000; Dostal et al., 2009; Song et al., 2014, Hazarika et al.,
2016). However, all of the scheelite from the study area has Na
concentrations below the EPMA detection limit, effectively ruling
out substitution (1) above (Supplementary Data,Table S2). The
scheelite in the study area also contains low concentrations of
Nb (0.52–60.92 ppm, average = 9.84 ppm; Supplementary Data,
Table S3), suggesting that substitution (2) is also relatively insignif-
icant. This leaves substitution (3), which involves a site vacancy
with no ionic radii restrictions during this substitution, indicating
that all of the REE should have identical partition coefficients. This
suggests that if this is the dominant substitution mechanism for
the incorporation of the REE into the scheelite in the study area,
then the REE patterns of the resulting scheelite most likely reflect
the REE compositions of the ore-forming fluids (Ghaderi et al.,
1999). Type 1 scheelite has a similar REE pattern to the exoskarn
garnet in the study area, suggesting that this scheelite not only
inherited compositional characteristics from the hydrothermal
fluid that formed the deposit but also suggests that this hydrother-
mal fluid formed both the mineralization and the skarn assem-
blages in the study area (Fig. 14A). Scheelite Eu anomalies can
also be used to monitor variations in hydrothermal fluid redox con-
ditions (Song et al., 2019; Han et al., 2020). Ghaderi et al. (1999)
indicated that scheelite Eu budgets dominated by Eu
3+
will yield
samples that plot along a Eu
N
(Eu chondrite-normalized)/Eu*
N
[where Eu*
N
= (Sm
N
Gd
N
)
1/2
] = 1 line in a Eu
N
vs. Eu*
N
diagram
(shown as a dashed line in Fig. 14A). In contrast, samples with
higher Eu
N
/Eu*
N
values are indicative of formation from mineraliz-
ing fluids dominated by Eu
2+
. The Type 1 scheelite plots along the
Eu
N
/Eu*
N
= 1 line, indicative of formation from hydrothermal fluids
dominated by Eu
3+
(Fig. 14A; Ghaderi et al., 1999). However, the
Eu
N
/Eu*
N
values of the Type 2 scheelite are significantly higher
than this 1:1 line, with the Type 3 scheelite having Eu
N
/Eu*
N
val-
ues > 10 or even > 100 (Fig. 14A). This provides evidence of the
hydrothermal fluids associated with these different types of
scheelite formation changing from Eu
3+
-dominant to Eu
2+
-
dominant. The positive correlation between scheelite Eu anomalies
and Mo concentrations for all of the scheelite in the study area also
indicates that the Eu anomalies within this scheelite were also pre-
dominantly controlled by the fO
2
conditions of the hydrothermal
fluids associated the Qiaomaishan deposit (Fig. 14B), consistent
with the discussion above. All of this suggests that scheelite Mo
concentrations and Eu anomalies are both effective approaches to
determine variations in fO
2
conditions during the evolution of
hydrothermal mineralizing systems.
The U–Pb dating of scheelite requires minerals with relatively
high concentrations of U. However, rather than substituting into
the scheelite structure, U can also be present as U-rich mineral
inclusions within scheelite, limiting the application of the U–Pb
geochronometer or potentially yielding geologically insignificant
dates. The scheelite (QMS-29) selected for U–Pb dating in this
study is free of mineral inclusions and microfractures, as evidenced
by the flat and smooth spectra obtained during LA–ICP–MS single-
spot analysis (Fig. 15). This indicates that the U within this scheel-
ite is homogeneously distributed within the scheelite structure and
more importantly that the scheelite is free of U-containing micro-
inclusions. The concentrations of U within the scheelite from the
study area also negatively correlate with Mo concentrations and
positively correlate with variations in Eu anomalies (Fig. 14C, D),
both of which reflect variations in hydrothermal fluid oxygen
fugacity conditions. This indicates that the main control on the U
concentrations of the scheelite within the Qiaomaishan deposit is
variations in oxygen fugacity conditions during the evolution of
the mineralizing systems. Uranium has only two forms of U
4+
Fig. 13. Tera–Wasserburg diagrams outlining the U–Pb ages for garnet (A), apatite (B), and Type 3 scheelite (C) samples from the Qiaomaishan deposit analyzed during this
study.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
12
and U
6+
in minerals, and U
6+
usually occurs in the form of (UO
2
)
2+
in nature, indicating that U is a complex cation (Hazen et al., 2009).
The ionic radius of U
6+
is also so large that it cannot be isomorphic
substitution with any cation, but U
4+
can be incorporated into min-
erals by isomorphic substitution for Th
4+
,Zr
4+
, REE
3+
, and Ca
2+
(Liu
et al., 1984). This means that a decrease in the oxygen fugacity of
the hydrothermal system in the study area caused the U
6+
stable
complex cation to change to U
4+
, increasing the concentration of
U
4+
in the hydrothermal fluid and improving the ability of U
4+
to
undergo isomorphic substitution and hence incorporation into
Fig. 14. Diagrams showing variations in (A) Eu
N
and Eu*
N
, (B) Eu/Eu* and Mo concentrations, and U concentrations versus (C) Mo and (D) Eu/Eu* within scheelite formed
during the different stages of mineralization within the Qiaomaishan deposit.
Fig. 15. Representative examples of single spot LA–ICP–MS data showing variations in the counts per second (CPS) data associated with variations in Ca, W, Mo, and U
concentrations within scheelite from the study area.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
13
minerals precipitating from this fluid. Minerals formed under such
low oxygen fugacity conditions therefore have higher U contents
than those formed under high oxygen fugacity conditions.
6.2. Timing of mineralization in the Qiaomaishan skarn Cu–W deposit
and the reliability of scheelite U–Pb dating
The spatial and paragenetic relationships between the intru-
sions, alteration, and mineralization within the study area indicates
that the formation of the QMS deposit is genetically associated with
a porphyritic granodiorite intrusion. Previous research (Li et al.,
2019) reported a zircon U–Pb age of 139.5 ± 1.2 Ma (MSWD = 0.3,
N= 23) for intrusion, which is within uncertainty of the exoskarn
garnet analyzed during this study (138.4 ± 1.0 Ma; Fig. 13A). The
apatite yielded a well-defined lower intercept age of 139.6 ± 3.3 M
a(Fig. 13C) that is again within uncertainty of the zircon U–Pb age
for the intrusion as well as within uncertainty of the garnet U–Pb
age reported during this study. These ages indicate that the
hydrothermal and mineralizing events recorded within the QMS
deposit are related to the emplacement of the intrusion.
The fact that the apatite and scheelite dated during this study
are from the same sample and have intimate paragenetic and con-
tact relationships (Fig. 10D–J) indicates that the dating results of
this scheelite should yield a consistent age with the apatite. The
scheelite yielded a lower U–Pb intercept age of 138.6 ± 3.2 Ma
(Fig. 13E), which is within uncertainty of the age of the apatite
and the garnet within the deposit. This demonstrates the useful-
ness of scheelite U–Pb dating of mineralizing systems and indicates
that geologically meaningful ages can be obtained using this
approach.
6.3. Potential applications of scheelite U–Pb dating
This study provides a robust approach to scheelite dating by
including discussion of ore deposit geology, the relative timing of
different stages of hydrothermal alteration and scheelite forma-
tion, mineral paragenesis and contact and cross-cutting relation-
ships, as well as analytical methods and instrument parameters.
This study also constrains the timing of emplacement of the intru-
sion (zircon) as well as the timing of formation of skarn minerals
such as garnet and apatite (from the same sample as the scheelite).
All of this allows the assessment of the reliability of the U–Pb
scheelite dating approach developed during this study. The consis-
tency of the ages obtained by these different methods within
uncertainty strongly suggests that scheelite can be used to directly
determine the mineralization age of a variety of different
hydrothermal deposits.
As mentioned above, scheelite commonly occurs in skarn-type
deposits, vein/stockwork deposits, porphyry deposits, orogenic
and intrusion-related gold, disseminated or greisen deposits as well
as breccia and brine/evaporite and hot spring deposits (Brown and
Pitfield, 2014; Haldar, 2020). The association between gold and
scheelite in orogenic gold deposits has long been recognized
(Goldfarb et al., 2005; Sciuba et al., 2020) and the direct dating of
hydrothermal gold mineralization is difficult as a result of the scar-
city of both suitable chronometers and in-situ techniques with suf-
ficient spatial resolution and precision (Rasmussen et al., 2006). The
research on the dating of scheelite in this study may provide a
potential solution to the precise determination of the timing of
mineralization and formation of scheelite-bearing gold deposits.
The widespread distribution of scheelite in other mineralizing sys-
tems also means that the further development of approaches to
date this scheelite will have broad applicability. The direct dating
of mineralization is essential for establishing robust genetic rela-
tionships between magmatic and mineralizing, tectonic, and other
processes as well as for the further refinement of ore deposit mod-
els and to further our understanding of the tectonic controls on ore
deposit formation within large metallogenic provinces (Li et al.,
2021b). This study confirms the accuracy and precision of scheelite
dating as well as the potential use of this approach for the deter-
mining of the absolute timing of mineral deposit formation (espe-
cially those associated with felsic magmas) either in addition to
other approaches to dating or as a stand-alone approach. The fact
that LA–ICP–MS can analyze U and Pb isotopes and trace elements
simultaneously also means that both the ages and trace and REE
concentrations of scheelite within deposits with multiple stages
(or events) of scheelite formation can be determined, allowing
not only the constraining of the timing of mineral deposit formation
but the evolution of mineralizing systems and conditions. This can
also provide insights into the presence of overprinting mineralizing
events within a given area. The in-situ LA–ICP–MS U–Pb dating of
scheelite requires few samples, meaning that deposits that not con-
tain economic scheelite mineralization but instead contain minor
amounts of this mineral can also be dated using this approach. It
is also important to note that the in-situ LA–ICP–MS U–Pb dating
of scheelite is more economical and faster than other more labor-
intensive methods, such as scheelite Sm–Nd dating. Further devel-
opments to potentially improve the accuracy and precision of the
U–Pb dating of scheelite may also enable the identification of differ-
ent stages of mineralization within a given mineralizing system,
allowing the identification of key times in gold, porphyry Cu–Mo–
Au, and other mineralizing systems, extending the implications of
this study way beyond skarn systems.
Although the in-situ LA–ICP–MS U–Pb dating of scheelite has
significant potential for use in a variety of mineralizing systems
and geological settings, it is still a new method that requires refine-
ment. The research undertaken on the Qiaomaishan deposit indi-
cates that not all types of scheelite are suitable for dating. This
means that the trace element analysis of samples prior to U–Pb
dating to screen out samples with higher U concentrations that
are suitable for use with his technique can improve the chances
of successful dating and the genesis of accurate and reliable scheel-
ite U–Pb ages.
7. Conclusions
(1) Dating of mineralization within the Qiaomaishan deposit
using multiple approaches (garnet, apatite scheelite) yields
ages that are consistent within uncertainty and are also
within uncertainty of a previously obtained zircon U–Pb
date for a mineralization-related intrusion in this area. This
indicates that the Qiaomaishan deposit formed
at 139 Ma and is closely related to the emplacement of a
porphyritic granodiorite intrusion in this area.
(2) The three types of scheelite in the Qiaomaishan deposit
recorded the evolution of the ore-forming fluids within this
mineralizing system including a drop in oxygen fugacity
conditions over time. The main factor that controlled the
increase in the U concentrations (and hence usefulness for
dating) of the scheelite in the study area was this decrease
in oxygen fugacity, generating the high U scheelite that is
a prerequisite for in-situ LA–ICP–MS U–Pb dating.
(3) In-situ LA–ICP–MS U–Pb dating of scheelite is an approach
with broad applicability that yields robust, precise, and
accurate results faster and more economically than other
approaches (e.g., scheelite Sm–Nd dating). However, obtain-
ing accurate and reliable ages requires detailed knowledge
of the ore deposit being studied as well as the correct selec-
tion of samples suitable for dating.
Y. Li, F. Yuan, S.M. Jowitt et al. Geoscience Frontiers 14 (2023) 101459
14
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgments
This research was financially supported by the National Natural
Science Foundation of China (Grant Nos. 41820104007, 91962218)
and the China Scholarship Council (Grant No. 201906690036). We
thank Dr. Guangxian Liu, Dr. Xunyu Hu, the Yanduzhongshi Geo-
logical Analysis Laboratories Ltd., the Comprehensive Geological
Brigade of East China Metallurgical Geographical Prospecting
Bureau, and the Huatong Mining Co. Ltd. for assistance and support
during fieldwork and analysis.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.gsf.2022.101459.
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