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Images of hydrothermal alteration mineral assemblages from Assarel. (a) Rock with propylitic alteration: groundmass made up of quartz, albite, epidote, sericite and chlorite (sample AS6). (b) Mafic phenocryst (probably amphibole) substituted by chlorite and epidote in a rock with propylitic alteration (sample AS5). (c) Intergrowth of calcopyrite, pyrite, sericite, and chlorite in a rock with sericitic-chloritic alteration (sample AS18). (d) Pervasive argillic alteration with diaspore, illite, and fine-grained pyrite mineralization (sample AS14). (e) Disseminated pyrite in a rock with sericitic alteration (sample AS30). (f) Sericitic alteration, with sericite filling a vugg in a quartz-rich rock (sample AS30). Transmitted light. (a,c-f)-crossed nicols; (b)-parallel nicols. Abbreviations: cpy-chalcopyrite, chl-chlorite, dsp-diaspore, ep-epidote, py-pyrite, qtz-quartz, ser-sericite.
Source publication
A petrographic investigation of ore samples from the Assarel porphyry copper deposit in the Srednogorie metallogenic zone (Bulgaria) constrains the setting and character of precious metals (Au, Ag, PGE) and related minerals within the deposit. This work supports renewed interest in understanding the deportment of precious metals and provides minera...
Contexts in source publication
Context 1
... phenocrysts in porphyritic wall rocks are partly replaced by epidote, albite, sericite and clay minerals (Figure 4a). There is no evidence of previous potassic alteration of feldspars. ...
Context 2
... is no evidence of previous potassic alteration of feldspars. Chlorite, epidote and opaque minerals totally replace mafic mineral phenocrysts (probably amphibole) where present ( Figure 4b). Chlorite, in association with rutile and titanite, also occurs as disseminated grains in the groundmass or along the margins of mineralized fissures and quartz veinlets. ...
Context 3
... define this alteration as sericitic-chloritic, considering that most key minerals of propylitic alteration type (e.g., epidote, albite, calcite) are not found in these rocks. The mineralization consists of chalcopyrite, pyrite and lamellar hematite, frequently being intergrown with chlorite and sericite and filling veinlets and cracks (Figures 4c and 5b,c). Chalcopyrite replaces and surrounds hematite (Figure 5c), forming rims and filling the cracks of hematite. ...
Context 4
... assemblage is found in rocks with relatively intense argillic alteration, dominated by clay minerals (Figure 4d). The samples of rocks with argillic alteration (sometimes overprinting sericitic alteration) commonly contain fine-grained pyrite and chalcopyrite (<0.2 mm), without magnetite or hematite (Figure 5d). ...
Context 5
... general, these inclusions are distributed in the peripheral parts of pyrite grains (Figure 5e). Although the host rock is mainly made up of quartz and sericite (Figure 4e,f), a clay-rich argillic overprint is also locally present. Primary igneous texture of the host rock is typically completely obliterated. ...
Citations
... Recent studies by Cioacă et al. (2020) indicate the occurrence of Au-, Ag-, Bi-, Te-, and Se-bearing minerals as minute inclusions in pyrite and chalcopyrite from the main chalcopyrite-pyrite ore assemblages and in the upper epithermal and supergene alteration zones. Platinum-group elements are scarce and reported as rare Pd-bearing tellurides occurring in pyrite. ...
The supply of European critical raw materials (CRMs) does not currently meet the European demand. This gap is predicted to increase, making Europe even more dependent on outside suppliers. AGEMERA is a project to help tackle this strategic problem by studying several CRM sites in Finland, Poland, Spain, the Balkans, and Zambia in different deposit types. To check the potential of the porphyry systems in Europe as a source of CRMs, the Assarel porphyry-Cu deposit was chosen as a test site. Here we present preliminary geochemical and mineral chemistry data for hydrothermal ore and alteration minerals in Assarel that reveal the potential of the deposit to source some CRMs as by-products. Further studies will combine the geochemical data with innovative geophysical methods for an improved deposit model and provide enhanced knowledge about effective exploration techniques for CRMs.
... From the alteration minerals, hydrothermal rutile concentrates trace elements like V (110-6700 ppm), Nb (2300-4600 ppm), Ta, W, and Sc; epidotes and APS (aluminium-phosphate-sulphate) minerals have elevated contents of REE, whereas hydrothermal chlorite (the Ti/Sr ratio) could potentially be used as an exploration fingerprinting tool. Recent studies by Cioacă et al. (2020) indicate the occurrence of Au-, Ag-, Bi-, Te-, and Se-bearing minerals as minute inclusions in pyrite and chalcopyrite from the main chalcopyrite-pyrite ore assemblages and in the upper epithermal and supergene alteration zones. Platinum-group elements are scarce and reported as rare Pd-bearing tellurides occurring in pyrite. ...
Global demand for critical raw materials (CRMs) continues to grow rapidly, mobilizing Europe’s domestic potential. Europe has a long tradition of mining and extractive activities of copper and base metals but is less successful in projects to source CRMs. A new Horizon Europe project called ‘AGEMERA: Agile Exploration and Geo-modelling for European Critical Raw Materials’ will contribute to the unlocking
of Europe’s CRM potential by conducting local state-of-the-art geological and geophysical surveys in six EU countries and one external country (Zambia). Mineral exploration targeting, sampling, modeling, and geophysical field trialing are planned in the project, whereas the exploration sites are chosen to ensure a variety of locations and mineral systems. One of the sites in AGEMERA is the Assarel porphyry Cu-Au deposit in Bulgaria.
... In addition to the above challenges, XCT-XRF scanning adds another step to the core characterization procedure of an exploration or mining operation (see also Cioacȃ et al., 2020). However, scanning (1,500 m at 3 m/h) and subsequent digital logging (~25 m/h) of a moderate amount of core at Lovisa has provided a significantly enhanced level of structural and mineralogical-geochemical detail not previously obtainable via conventional methods, thereby allowing for refinement of 3-D geologic models at multiple scales. ...
We present the results of a pilot study that integrates automated drill core scanning technology based on simultaneous X-ray computed tomography (XCT) and X-ray fluorescence (XRF) analyses to provide high-spatial-resolution (<0.2 mm) information on 3-D rock textures and structures, chemical composition, and density. Testing of its applicability for mineral exploration and research was performed by scanning and analyzing 1,500 m of drill core from the Paleoproterozoic Lovisa stratiform Zn-Pb sulfide deposit, which is part of a larger mineral system also including Cu-Co and Fe-(rare earth element) mineralization, hosted by the highly strained West Bergslagen boundary zone in south-central Sweden.
The obtained scanning data complements data derived from structural field mapping, drill core logs, and chemical analysis as well as from multiscale 3-D geologic modeling at Lovisa. Data integration reveals macro- and mesoscopic folding of S0/S1 by asymmetric steeply SE-plunging F2 folds and N-striking vertical F3 folds. Stretching lineations, measured directly from the scanning imagery, trend parallel to F2 fold hinges and modeled ore shoots at the nearby Håkansboda Cu-Co and Stråssa and Blanka Fe deposits. The textural character of the Lovisa ore zones is revealed in 3-D by XCT-XRF scanning and highlight remobilization of Zn and Pb from primary layering into ductile and brittle structures. The downhole bulk geochemical trends seen in scanning and traditional assay data are generally comparable but with systematic variations for some elements due to currently unresolved XRF spectral overlaps (e.g., Co and Fe).
The 3-D deformation pattern at Lovisa is explained by D2 sinistral transpression along the West Bergslagen boundary zone in response to regional north-south crustal shortening at ca. 1.84–1.81 Ga. Local refolding was caused by D3 regional east-west crustal shortening resulting in dextral transpression along the West Bergslagen boundary zone, presumably at ca. 1.80–1.76 Ga. Based on polyphase ore textures and modeled ore shoots aligned to F2 fold hinges, we postulate that D2 and D3 transpressive deformation exerted both a strong control on ore remobilization and the resulting orebody geometries at Lovisa and neighboring deposits within the West Bergslagen boundary zone.
We conclude that the combined XCT-XRF drill core scanning technique provides a valuable tool for 3-D ore and rock characterization, generating continuous downhole data sets, with the potential for increasing precision and efficiency in mineral exploration and mining.
... The Assarel copper mine in Bulgaria is one of four sulfide deposits chosen as pilot sites to test new drill core scanning and ore sorting technology as part of the Horizon 2020 X-Mine project (e.g. Cioacă et al. 2020). A key aim of X-Mine is to validate the GeoCore X10 (GX10), which is a drill core scanner that uses simultaneous X-ray computed tomography and X-ray fluorescence (XCT-XRF) analysis to produce downhole chemical and density data, and 3D XCT imagery (e.g. ...
... The Assarel porphyry Cu-Au deposit is located in the Panagyurishte mining district of west-central Bulgaria, part of the larger Srednogorie magmatic-metallogenic zone (Fig. 1A). The deposit represents a complex magmatic-hydrothermal system that formed during the Late Cretaceous as part of an evolving continental volcanic arc (Peytcheva et al. 2007;Gallhofer et al. 2015, Cioacă et al. 2020. Deposit host rocks are variably altered Late Carboniferous intrusive rocks, and syn-mineralization andesites and dioritic to granitic subvolcanic rocks (Fig. 1B-C; Strashimirov et al. 2003). ...
... Previous studies have linked different ore and vein mineral assemblages to the main alteration types and their distributions (e.g. Strashimirov et al. 2003;Cioacă et al. 2020). Propylitic alteration is associated with chalcopyrite + pyrite + magnetite ± bornite occurring in veinlets and as fine-grained disseminations. ...
The thick laterite developed over the PGE-bearing ultramafic rocks of the Owendale Alaskan-Urals complex provides an ideal environment in which to address the problem as to whether or not Pt-Fe nuggets are formed during lateritization. This is an important issue to settle as Pt placers have been major Pt producers and continue to produce significant amount of Pt. Some of the Owendale laterite profiles have high Pt but low Cu contents while others have both high Pt and Cu contents. Heavy mineral concentrates were prepared from ~1 kg Reverse Circulation drill chips from metre long drill intersections of both types of laterites. Only 5 of the 60 samples processed contained any PGM even though many of the samples contained more than 1 g/t Pt. The largest PGM found was only ~100 µm in length and the bulk of the PGM found were < 20 µm. PGM textures indicate that the Pt-Fe and Pt-Cu-Fe alloys were destroyed during lateritization with the Pt
liberated forming Pt nanoparticles, Pt-oxides, Pt nanoparticles, or being adsorbed by the Fe-oxide hosts. No evidence was found for the growth of PGM nuggets.
... Porphyry-type deposits are the major sources of copper (Cu) and molybdenum (Mo)-approximately 60% of Cu and 50% of Mo are annually produced from these deposits [1][2][3]. Apart from Cu and Mo, precious metals (e.g., gold (Au), silver (Ag), and platinum group elements (PGEs)) and several strategic/high-tech elements (e.g., rhenium (Re), tungsten (W), bismuth (Bi), indium (In), tellurium (Te), and selenium (Se)) may reach economic concentrations, thus being recovered as by-products during porphyry ore processing [3,4]. Typically, porphyry-type deposits are developed via a series of processes: ...
Porphyry-type deposits are the major sources of copper and molybdenum, and flotation has been adopted to recover them separately. The conventional reagents used for depressing copper minerals, such as NaHS, Na2S, and Nokes reagent, have the potential to emit toxic H2S gas when pulp pH was not properly controlled. Thus, in this study the applicability of microencapsulation (ME) using ferrous and phosphate ions as an alternative process to depress the floatability of chalcopyrite was investigated. During ME treatment, the use of high concentrations of ferrous and phosphate ions together with air introduction increased the amount of FePO4 coating formed on the chalcopyrite surface, which was proportional to the degree of depression of its floatability. Although ME treatment also reduced the floatability of molybdenite, ~92% Mo could be recovered by utilizing emulsified kerosene. Flotation of chalcopyrite/molybdenite mixture confirmed that the separation efficiency was greatly improved from 10.9% to 66.8% by employing ME treatment as a conditioning process for Cu-Mo flotation separation.
This study encompasses the ore mineralogy, textures and sulphide trace element chemistry of the Palaeoproterozoic Lovisa stratiform Zn-Pb deposit and the stratigraphically underlying Lovisa Fe Formation in the Bergslagen ore province (Sweden). We investigate the relative timing of formation and subsequent modifications of its ores in relation to the c. 1.87-1.80 Ga Svecokarelian orogeny. The Lovisa Zn-Pb deposit consists of several different ore types. The massive sphalerite-galena ore is distinctly deformed, exhibiting a multiple-scale “ball ore” texture with rounded silicate clasts within a deformed, fine-grained sulphide matrix. Underlying the massive ore is a locally folded, sphalerite-rich laminated ore, interpreted to represent a metamorphosed relict primary lamination. Several generations of sphalerite-galena fracture fillings and veins occur adjacent to the main ore zones and they cross-cut early ductile structures and metamorphic features. The trace element signatures of the sphalerite-galena infillings generally mimic those of the two main ore zones, thus supporting an origin by localised remobilisation of the primary sulphide ore and demonstrating limited trace element redistribution during this process. In contrast, discrete sulphosalt-rich fracture fillings cross-cutting earlier galena-chalcopyrite-rich fracture fillings and veinlets in the Lovisa Fe Formation suggest a significant but still relatively localised redistribution of metals. Trace element mapping of sulphides from the Lovisa Zn-Pb deposit reveals that inclusion-free overgrowths on pyrite crystals are locally Co-enriched compared to the cores, which resulted from the redistribution of Co during late metamorphic processes. Combined textural and geochemical evidence suggest that the originally syngenetic exhalative sulphide ore at Lovisa was locally strongly affected by polyphase deformation and remobilisation. This was initiated during the first stage of amphibolite facies grade regional metamorphism and deformation (D1, c. 1.87-1.85 Ga) but is mostly evident from the later stages (D2) and the evolution to retrograde and brittle conditions (c. 1.83-1.80 Ga and later).
Porphyry deposits are an important source of copper and their value may be upgraded by minor contents of precious metals, if they are extractable. The mechanisms for enrichment of precious and base metals in these systems are not well understood. This study investigates the deportment of trace metals in the Ann-Mason porphyry deposit, including gold, silver, palladium, mercury, lead and bismuth. Petrographic and geochemical data are integrated to characterise the size and habit of minerals, the host mineral assemblages, and their association with alteration assemblages. Ann-Mason is one of several ore deposits hosted by the Yerington batholith in Nevada, and is being assessed for copper extraction from bornite and chalcopyrite ore assemblages, associated with potassic alteration. Mineralisation assemblages at Ann-Mason have been categorised as chalcopyrite-bornite, chalcopyrite-pyrite and pyrite>chalcopyrite zones. Limited two-metre assay data indicates that gold is most closely associated with bornite, although it is found in all three mineralisation zones. Analysis by SEM-EDS shows that trace elements are mostly present as microparticles hosted by sulfide minerals. Of the 438 grains measured, 89% are hosted by a sulfide mineral, with 68% hosted by bornite. Silver is most commonly present as hessite and gold as electrum, hosted by bornite and associated with potassic alteration. Palladium, mercury and bismuth are most commonly observed as telluride and selenide minerals. Palladium minerals are associated with potassic alteration, while mercury and bismuth minerals are mostly found with sericitic alteration. High fineness native gold is observed as three round blebs hosted by pyrite or silicates. Observations suggest that the trace metals in the chalcopyrite-bornite zone may have been incorporated by bornite and chalcopyrite, and exsolved upon cooling. In the chalcopyrite-pyrite and pyrite>chalcopyrite zones, the trace metals may have been deposited directly from a mineralising hydrothermal fluid and incorporated into the growing sulphide minerals. These findings have implications for the paragenesis of porphyry deposits, as well as for the milling processes that would be needed to extract precious metals at the Ann-Mason porphyry deposit.
