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Background. Artisanal and small-scale miners in Bolivia release on the order of 120 tons of mercury annually. The mercury finds its way to the Amazon with catastrophic consequences for the biosphere. A project aimed at reducing the release of mercury was carried out in 2013 and 2014.
Objectives. The project had two objectives: to test whether the m...
187Rhenium-187Os model ages are used to infer the timing of crust-mantle differentiation events and evolution of lithospheric mantle. However, ancient samples often have long and complex histories of metamorphism, metasomatism and deformation that may be problematic if these processes caused disturbance the Re-Os system. Such processes have been sh...
The Archean craton of West Greenland consists of many fault-bounded Eoarchean to Neoarchean tectonic terranes (crustal blocks). These tectonic terranes are composed mainly of tonalite-trondhjemite-granodiorite (TTG) gneisses, granitic gneisses, metavolcanic-dominated supracrustal belts, layered anorthositic complexes, and late- to post-tectonic gra...
Partial melting of the Earth’s mantle is a key process in
the generation of crustal material and the formation of
continents1. Crustal samples record the generation of crust
up to 4.4 billion years (Gyr) ago2–9, yet the complementary
record in the mantle extends to only 3.3Gyr ago1, with sparse
evidence for differentiation occurring 3.9–4.1Gyr ago1...
Mercury pollution from small-scale gold mining poses a serious threat to the global and local environment. Recycling of mercury for small-scale miners has been introduced over decades in Tanzania with little success. The environmentally benign borax gold extraction method invented more than thirty years ago in the Philippines and presently used by...
The Fiskenæsset Complex, SW Greenland, contains the world's best preserved Archean (∼2970 Ma) layered anorthosite, leucogabbro, gabbro, and ultramafic association. The complex was emplaced into Archean oceanic crust distal from continental lithosphere and later intruded by tonalites, trondhjemites and granodiorites (TTG) constituting Archean contin...
The Mesoarchean Fiskenæsset Complex was emplaced as multiple sills and dykes of magma and crystal mush into oceanic crust, forming an association of ca. 550-meter-thick layered anorthosites, leucogabbros, gabbros, hornblendites, pyroxenites, dunites, and peridotites. The complex was intruded by tonalites, trondhjemites and granodiorites (TTG), and...
Background. More than ten million small-scale miners (SSM) worldwide use mercury to extract gold, releasing large amounts of the toxic element into the environment. Alternatives to mercury have been suggested over the years to little avail. A group of miners in the Philippines has demonstrated that borax, when used as a flux for smelting gold out o...
Background. More than ten million small-scale miners (SSM) worldwide use mercury to extract gold, releasing large amounts of the toxic element into the environment. Alternatives to mercury have been suggested over the years to little avail. A group of miners in the Philippines has demonstrated that borax, when used as a flux for smelting gold out o...
In Inglefield Land, northwest Greenland, a new glacial feature has been found, consisting of well-defined circles and rings ranging in size from a few metres to about 80 m in diameter and in colour from black to pink. More than 300 circles and rings are known. They are composed of slightly rounded boulders, cobbles, and pebbles frequently overgrown...
This study reviews the geochemical characteristics of Eoarchean to Mesoarchean ultramafic to mafic volcanic rocks (now amphibolites) in SW Greenland and compares them with those of Cenozoic oceanic island arc basalts, to evaluate Archean subduction zone petrogenetic processes. Emphasis is placed on the Th–REE–HFSE (Zr, Ti, and Nb) systematics of th...
The Fiskenæsset Complex, SW Greenland, is one of the best preserved layered Archean intrusions in the world, consisting of an association of ca. 550-meter-thick anorthosite, leucogabbro, gabbro, and ultramafic rocks (dunite, peridotite, pyroxenite, and hornblendite). Despite poly-phase deformation and amphibolite to granulite facies metamorphism, p...
The authors have established a method of determining mercury and gold in severely polluted environmental samples using prompt gamma-ray analysis (PGA) and instrumental neutron activation analysis (INAA). Since large amounts of mercury are constantly being released into the environment by small-scale gold mining in many developing countries, the mer...
Thin tourmaline-rich layers closely associated with strata-bound tungsten mineralization occur in layered amphibolites and metasediments of the Archaean Malene supracrustals in West Greenland. Locally, tourmaline is intergrown with scheelite. Microprobe analyses showed that the tourmaline is of intermediate composition, between schorl and dravite,...
The Archean Fiskenæsset Complex, SW Greenland, consists of an association of ca. 550-meter-thick layered anorthosite, leucogabbro, gabbro, and ultramafic rocks (peridotite, pyroxenite, dunite, hornblendite). The complex was intruded by tonalite, trondhjemite, and granodiorite (TTG) sheets (now orthogneisses) during thrusting that was followed by se...
The solid planets assembled 4.57 Gyr ago during a period of less than 100 Myr, but the bulk of the impact craters we see on the inner planets formed much later, in a narrow time interval between 3.8 and 3.9 Gyr ago, during the so-called late heavy bombardment (LHB). It is not certain what caused the LHB, and it has not been well known whether the i...
New major and high-precision ICP-MS trace element data on the Neoarchean (ca. 2970 Ma) layered Fiskenæsset Complex and associated volcanic rocks, southern West Greenland, provide new constraints on the petrogenesis and geodynamic setting of the complex. The complex appears to have been emplaced as multiple sills of magma and crystal mush into ocean...
The Mesoarchean Ivisaartoq greenstone belt consists of tholeiitic pillow basalts, picrites, boninites, gabbroic to dioritic dykes and sills, actinolite schists and serpentinites. In addition, the belt includes volumetrically minor siliceous volcaniclastic sedimentary rocks, cherts, biotite schists, and quartzitic gneisses. Siliceous volcaniclastic...
The Ivisaartoq (ca. 3075 Ma) and Ujarassuit (ca. 3070 Ma) greenstone belts are the largest Mesoarchean supracrustal lithotectonic assemblages in the Nuuk region, SW Greenland. Both greenstone belts underwent polyphase deformation and amphibolite facies metamorphism, and were in due course variously dismembered. Pillow lavas, pillow breccia, magmati...
The Late Heavy Bombardment (LHB) period is the narrow time interval between 3.8 and 3.9 Gyr ago, where the bulk of the craters we see on the Moon formed. Even more craters formed on the Earth. During a field expedition to the 3.8 Gyr old Isua greenstone belt in Greenland, we sampled three types of metasedimentary rocks, that contain direct traces o...
Mafic volcanic rocks in the 3.8–3.7 Ga Isua greenstone belt, southern West Greenland, contain randomly distributed 1 to 10-centimeters long white spheroidal structures. In this study, these structures are called ‘ocelli’. In the western part of the belt, ocelli-bearing lavas are enclosed in basaltic to picritic flows (MgO = 9–21 wt.%) with a subduc...
The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt consists dominantly of variably deformed and metamorphosed mafic to ultramafic flows (basalts to picrites). In addition, there are minor serpentinites, gabbros, clinopyroxene-rich cumulates, and volcaniclastic and siliciclastic sedimentary rocks. Primary volcanic structures such as pillows an...
In this review we summarize the major lithological and geochemical characteristics of the Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt, Nuuk region, southern West Greenland. In addition, the geological characteristics of the Ivisaartoq greenstone belt are compared with those of other Archean greenstone belts in the area. The Ivisaartoq gree...
The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt contains well-preserved primary magmatic structures, such as pillow lavas, volcanic breccias, and clinopyroxene cumulate layers (picrites), despite the isoclinal folding and amphibolite facies metamorphism. The belt also includes variably deformed gabbroic to dioritic dykes and sills, actinol...
Widespread gold showings have been found in an Archean greenstone belt on Storø in Godthåbsfjord, West Greenland. The Storø Greenstone Belt (SGB) comprises metasedimentary and metavolcanic rocks with minor magnetite-rich bands. Gold mineralization is hosted by amphibolites, mica schists and garnetite rocks. Gold occurs in various mineral associatio...
The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt in southern West Greenland includes variably deformed and metamorphosed pillow basalts, ultramafic flows (picrites), serpentinized ultramafic rocks, gabbros, sulphide-rich siliceous layers, and minor siliciclastic sedimentary rocks. Primary magmatic features such as concentric cooling-cracks...
Two lightning impacts are described from an area near the Inland Ice in West Greenland. The first lightning blasted an outcrop of metacherts. It subsequently split into two branches, which traversed rock outcrops and boulders, leaving behind two white almost straight lines, 30 m and 14 m long, respectively, where all lichens and plants were burned...
Fluid inclusions in quartz globules and quartz veins of a 3.8–3.7 Ga old, well-preserved pillow lava breccia in the northeastern Isua Greenstone Belt (IGB) were studied using microthermometry, Raman spectrometry and SEM Cathodoluminescence Imaging. Petrographic study of the different quartz segregations showed that they were affected by variable re...
Carbon and sulfur isotopes have been measured on samples from four Archean greenstone belts dating from 3.8 Ga to 2.7 Ga, in order to trace metabolic changes as life evolved over this one-billion-year period. In the Isua Greenstone Belt (3.8 Ga), Greenland, δ34S in sulfide minerals from sedimentary sequences range from -3.8‰ to +3.4‰. δ13Credmeasur...
Carbon and sulphur isotopes have been analysed in mineralization from two Archaean greenstone belts at 3.8 Ga and 2.7 Ga, with the aim of distinguishing between the inorganic and organic processes that occurred. Despite an obvious overprinting by metamorphism (in the early belt), or hydrothermal fluids, there are convincing differences between the...
A large number of metamorphosed ultramafic bodies are found in the region SW of the Isua Greenstone Belt in southern West Greenland, enclosed in Archaean banded tonalitic gneisses. These enclaves of dunite and harzburgite range in size from a few to several hundred meters. The Ujarassuit Nûnat layered body occurs as a large enclave (800 m×100 m) en...
Spherical objects, identified as microfossils and named Isuasphaera isua (Pflug), were reported in 1978 from a chert in the 3.7–3.8Ga Isua Greenstone Belt (IGB). Soon afterwards the biological nature of these objects was questioned on a number of grounds by several authors.Following renewed, recent claims for biogenicity, the locality has been revi...
The ˜3.75 Ga Isua Greenstone Belt (West Greenland) host remnants of the oldest oceanic crust on Earth. The rocks comprise mafic pillow lavas, banded iron formation and metasediments. They have been repeatedly deformed and metamorphosed up to high-amphibolite facies conditions. In low strain zones well preserved primary depositional structures are s...
Pillow basalts from the early Archean (3.7 to 3.8 Ga) Isua greenstone belt, West Greenland, are characterized by well-preserved rims and concentric core structures. The pillow rims and cores have different mineral assemblages, and chemical and isotopic compositions. The rims have systematically higher contents of Fe2O3, MgO, MnO, K2O, Rb, Ba, Ga, Y...
Massive chromitite, banded chromitite and disseminated chromite grains are found in a similar to3800 Ma layered ultrabasic body in West Greenland. The major part of the ultrabasite is dominated by dunite. In the upper exposed part, harzburgite and sheets of gabbro-anorthosite occur. Chromite grains in dunites, and in massive and banded chromitites...
An early Archaean (>3·81 Ga) chromitite–ultramafic layered body from the Ujaragssuit nun a ˆ t area, west Greenland, may represent the Earth’s oldest chromitite. The layered body occurs as a large xenolith (800 m × 100 m) entrained within tonalitic gneisses and preserves primary igneous layering and textures. New Re–Os and Pb–Pb isotope results sup...
A low-strain domain has been identified in the metamorphosed, mostly highly deformed volcanic and sedimentary rocks of the early Archaean Isua supracrustal belt. This domain contains well-preserved volcanic and sedimentary features, including basaltic pillow lavas, pillow breccia, heterogeneous volcanic breccia, amygdules in metabasalt, and polymic...
Localised low-strain domains in the ∼3.75 Ga Isua Greenstone Belt, West Greenland, contain a wealth of well-preserved primary structures. These include pillow lavas with dark, fine-grained cooling rims, pillow breccias, debris flows and conglomerates. Here we describe quartz globules from a relatively undeformed pillow breccia, which contains unstr...
New structural and stratigraphic mapping in the Isua greenstone belt, West Greenland has revealed that the exposed lithologic succession is quite different to that depicted in earlier studies. The key to a better understanding of the stratigraphy has been the recognition of intense strain and metasomatic effects combined with ductile fault structur...
An early Archaean greenstone belt and mid-Archaean supracrustal rocks in central West Greenland host a number of significant mineral occurrences that have recently been targets for exploration, which has included diamond drilling. Diamond drilling in the ca 3750-m.y. Isua greenstone belt detected a large hematite orebody concealed beneath the Inlan...
The Zn-spinel gahnite has been discovered in the ~3.75 Ga Isua Greenstone Belt, West Greenland. It is light blue-green to colourless in hand specimen and colourless in thin section as opposed to most other gahnites which are dark green to brown. The gahnites from Isua have very low Fe and Mg contents, and their compositions are thus close to the en...
The Zn-spinel gahnite has been discovered in the ~3.75 Ga Isua Greenstone Belt, West Greenland. It is light blue-green to colourless in hand specimen and colourless in thin section as opposed to most other gahnites which are dark green to brown. The gahnites from Isua have very low Fe and Mg contents, and their compositions are thus close to the en...
Ludwigite from B-bearing iron ores in the Bergslagen area of central Sweden and in the coastal area north of Stockholm has been studied using chemical and single-crystal diffraction techniques. Structure refinements, completed for three crystals showing slightly different Al contents, in the space group Pbam (agreement factor: 2.42 ≤ R ≤ 2.79) indi...
Parallel with ongoing exploration of the planets, particularly those that might harbor life, attention is again focusing on deciphering the origins of life on Earth. Multidisciplinary research on ancient rocks in Greenland has become an important part of that focus and may clarify the environmental conditions of the Earth's surface at a time when t...
Yuanfuliite crystals, ideally MgFe3+O(BO3), i.e. the Fe3+ analogue of warwickite Mg1..5 Ti0.5O(BO3), have been found in ultramafic rocks of Precambrian age in Inglefield Land (North-West Greenland). Structure refinements (space group Pnma) of two crystals with slightly different composition (agreement factors R = 0.023 and 0.025, respectively), hav...
The Isua belt of 3.8–3.7 Ga metavolcanic and metasedimentary rocks, is located 150 km north-east of Nuuk, within the Archaean gneiss complex of West Greenland. Most of this gneiss complex consists of late Archaean rocks with a minor component of early Archaean age, including the oldest known supracrustal rocks on Earth. The Isua belt contains the b...
Warwickite constitutes about 5% of an outcrop of metamorphosed ultramafic rocks of Precambrian age in North-West Greenland. It occurs as slender grains, several millimetres long, and in anhedral grains up to 5 mm in size, together with forsterite, pleonaste, phlogopite, magnetite ± tourmaline. Post-metamorphic alteration of warwickite produced a ne...
The boron isotope composition of different occurrences of tourmalines in the 3.8-Ga-old Isua (West Greenland) supracrustals has been analysed by ion microprobe. Tourmalines in the mafic volcaniclastics have δ11B values between −12.6 and +5.8% with a mean at −3.2±5.1%. These values are close to the values previously reported for tourmalines in the I...
In Archaean supracrustal rocks in West Greenland komatiitic and tholeiitic rocks have undergone alteration by circulating hydrothermal solutions, whereby the rocks were partly transformed into calc-silicate assemblages. The alteration, which also formed extensive stratabound scheelite mineralizations, took place partly at the sea floor and partly b...
Tourmalinites have been found in the early Archaean Isua supracrustal belt in mafic sediments representing metamorphosed mafic tuffs. The tourmalinites are spatially associated with sulphides and an iron-formation consisting of alternating magnetite and quartz bands. Tourmalines are also found as scattered grains in the mafic tuffs as well as in a...
Extensive scheelite-bearing calc-silicate zones with elevated contents of chromium, nickel, copper, zinc, yttrium and barium are found in Archaean supracrustal rocks of the Nuuk area, West Greenland. The calc-silicate zones are largely stratabound and occur in mafic and ultramafic metavolcanic rocks. The calc-silicates are interpreted as amphibolit...
In the early Archaean Isua supracrustal belt, West Greenland, a banded iron-formation is closely associated with stratabound copper sulphides. In banded amphibolites of the supracrustal sequence, scheelite occurrences are known. The scheelite, which occurs as tiny grains arranged parallel to the banding of the amphibolites, is clearly stratabound....
Isotopic ratios of Ce and Nd and abundances of rare earth elements (REEs) and Ba are reported for the iron-formations of the Archean Isua and Malene supracrustals, West Greenland. It is suggested that the Sm-Nd system of the Isua iron-formations was disturbed by metamorphisms at 1680 Ma (oxide facies iron-formation) and 2740 Ma (carbonate facies ir...
Close to the town Aasiaat/Egedesminde supracrustal rocks outcrop on some small islands situated around the position 68°46'N and 52°38'W. The largest of these islands, Isuamiut, is barely a few kilometres long and the islands are situated more than 10 km from the mainland. an Isuamiut two tourmaline-rich layers or tourmalinites have been found (Elli...
In the Archaean Malene supracrustal rocks of West Greenland different types of stratiform tourmalinites have been found. The present article describes schistose anthophyllite-rich tourmalinites hosted in anthophyllite-cordierite schists. It is shown that the boron is of submarine exhalative origin and was absorbed from seaweater by clay minerals. T...
In the Archaean Malene supracrustal rocks, West Greenland, small horizons of iron-formation occur. They are rarely more than a few metres wide and can be traced with intervals for several hundreds of metres along strike. The iron-formation is mainly silicate and sulphide facies, with high contents of trace elements such as 1.1% Zn, 0.18% Mo, 0.12%...
Five samples from the Isua locality B (65°07′N, 50°12′W) additional to those previously reported by P.W.U. Appel and coworkers have been assayed for Pb isotope ratios. Whilst giving close support to data on the two samples which were reported for this locality, the new information can be seen to define two very good, but short, regression lines wit...
This orthoamphibole, which consists of alternating lamellae of anthophyllite and gedrite, occurs in metasedimentary and metavolcanic rocks at several localities within approx 30 miles (50 km) of Nuuk. Attractive cabochons are marketed under the trade name nuummite. -R.V.D.
The Malene supracrustal rocks form large enclaves in the late Archaean Nûk gneisses within an area of at least 36 000 km2 on the west coast of Greenland and have been repeatedly deformed and metamorphosed under amphibolite facies conditions. Stream sediment sampling has shown that scheelite occurs in the supracrustal enclaves throughout the area. I...
Scheelite in the Godthåbsfjord area (fig. 1) was found in heavy mineral concentrates from stream sediments in 1982, and in situ scheelite was discovered in 1982 on Storø in Godthåbsfjord (Appel, 1983a). During 1983 further work was carried out on the islands of Storø and Sermitsiaq in Godthåbsfjord and on the Store Malene mountain next to Nuuk (God...
Recent work by the Geological Survey of Greenland (GGU) in the Godthåb (Nûk) area has revealed a large tungsten province with extensive scheelite mineralisation in the Archaean Malene supracrustal rocks (Appel, 1983, 1984). In the area between Godthåb and Frederikshåb Isblink several large supracrustal amphibolite belts occur (fig. 1). These are pr...
In the Archean of Western Greenland a tungsten province ca. 300 km long and up to 120 km wide has been discovered with extensive banded amphibolites containing up to 2% W and 0.16 ppm gold. The tungsten occurs as scheelite which is associated with tourmalinites and strata-bound tourmaline-rich layers in amphibolites of presumed tuffaceous origin an...
Gahnite occurs with magnetite, grunerite and sulphides in the Malena supracrustal belt. The average of 33 probe analyses gave Al2O3 58.18, FeO 10.50, ZnO 27.71, MnO 0.08, MgO 3.30, TiO2 0.00, SnO 0.00, = 99.77; a 8.101 A. Where the gahnite borders magnetite it has a brownish anisotropic rim or corona containing Ti and Sn; the average of 13 probe an...
As part of the regional stream sediment sampling programme in the Godthåb area (Appel, 1983, 1984),22 stream sediment samples were collected in the Isukasia area in 1983, of which 21 appeared to contain scheelite. In 1984 a one-week field programme was carried out towards the end of August in order to find in situ scheelite within the Isua supracru...
The discovery in 1982 of scheelite in stream sediments in the Godthåb area and in situ mineralisations in the early Archaean Akilia rocks on Storø in Godthåbsfjord (Appel, 1983) was followed up by field work in the summer of 1983. The regional stream sediment sampling programme was extended to Ameralik fjord, south af Godthåb, and to the inner part...
In the early Archaean Isua supracrustal rocks, tourmaline is found as either stratabound occurrences in conglomerates and impure dolomites or as a tourmaline-rich inclusion. This inclusion, which is approx 60% tourmaline, occurs as a fragment in metapelite and was presumably derived from pre-Isua rocks. An evaporitic sabkha origin is suggested for...
Gold-bearing sulphide mineralizations occur as conformable quartz layers, lenses and veins in basaltic greenstones; the gold occurs associated with arsenopyrite-pyrite, tennantite and chalcopyrite. Gold particles in the arsenopyrite-pyrite layers have a true fineness of approx 990, in the tennantite-rich veins approx 720 and in the chalcopyrite-qua...
The tungsten mineral scheelite has not previously been reported from the Godthåb area in West Greenland. The first indications of its presence were found in heavy mineral concentrates from a stream on Storø in Godthåbsfjord. Exploration for scheelite in Greenland is difficult. A systematic stream-sediment programme cannot be undertaken before mid-J...
The geology of the Godthåb area, West Greenland, has been studied for several decades, mainly by the Geological Survey of Greenland (GGU), but also by groups from British and other Universities. This work has resulted in a detailed understanding of most of the major rock forming events which have affected the area. However, one important aspect af...
In the pre-3.7 Ga old Isua supracrustal belt, West Greenland, a banded iron-formation occurs. The iron-formation can be subdivided into different facies according to composition and mineralogy, and these facies resemble the facies subdivision of younger Archaean and Precambrian iron-formations. The geochemistry of the Isua iron-formation indicates...
In the ca. 3.8 b.y.-old Isua supracrustal belt, West Greenland, pyrrhotite and chalcopyrite occur as strata-bound mineralizations in layered tuffaceous amphibolites and in an iron-formation. Mineralizations with more complex mineral assemblages comprising galena and sulphides of Ni, Sb, Cd, and Ag are of limited extent only. Field relationships, ra...
An international iron-formation reference sample is warranted as a basis for geochemical investigations of Precambrian iron-formations. A better knowledge of the geochemistry of iron formations will hopefully elucidate the long standing discussion on the genesis of iron-formations. The reference sample can furthermore be used in studies of deep-sea...
Tiny chromite grains were found in various facies of a banded iron-formation in the Isua supracrustal belt, West Greenland. The chromites have a peculiar composition with 0.1 % MgO. The Isua chromites resemble in size meteoritic chromite grains found in modern deep-sea sediments. The depositional environment of the Isua iron-formation indicates tha...
The sulfur contents and sulfur isotope ratios (δ34S) have been measured for samples collected from the Isua area of West Greenland in an effort to place narrower limits on the time of the rise of sulfate respirers during the Precambrian.The δ34S values of the Isua sediments (3.7 × 109 yr old) including the various facies of the banded iron-formatio...
One hundred and twenty-four carbonate samples from the meta-sedimentary sequence of the 3.7 × 109 yr old Isua supracrustal belt (W-Greenland) have yielded a δ13Ccarb average of −2.5 ± 1.7%. vs PDB and a δ18Ocarb average of +13.0 ± 2.5%. vs SMOW. The oxygen mean comes fairly close to the averages of other early Precambrian carbonates. The carbon ave...
In the pre-3,760-m.y.-old Isua supracrustal belt, West Greenland, copper sulfides with minor amounts of pyrrhotite are found
in sulfide, silicate, and carbonate facies iron-formation. In oxide facies iron-formation pyrite is the sole sulfide, occurring
in small quantities. In metamorphosed basaltic tuffs thin layers of chalcopyrite and pyrrhotite h...
FIELD relationships and geochronological data have shown that the metamorphosed supracrustal rocks of the Isua area are the oldest known components of the Archaean complex of West Greenland1-4. Rb-Sr, U-Pb and Pb/Pb ages in the range ∼ 3,700-3,800 Myr have been reported from various units within the Isua supracrustals5-9. One of us (P.W.U.A.) has r...
