Sorosite, Cu(Sn,Sb), a new mineral from the Baimka placer deposit, western Chukotka, Russian Far East
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Abstract:
Sorosite, ideally Cu(Sn5Sb), is a new mineral species from the Baimka gold-platinum- group mineral placer deposit, Chukotka, Russian Far East. It occurs as large subhedral to euhedral crystals (0.1-0.4 mm in length), hexagonal in cross section, minute crystals (≤ 15 μm, also hexagonal), and anhedral grains. Sorosite forms inclusions in Sb-bearing native tin, is often intergrown with stistaite (Sn1.12 - 1.13Sb0.87 - 0.88) and occurs with herzenbergite (SnS), native lead, and trace cassiterite. Sorosite is brittle with a microhardness VHN40;50 = 443.7 kg/mm2 (n = 3). No cleavage is observed. In reflected light, the large crystals are nearly white with a pinkish tint, whereas the microcrystals show a pronounced pinkish tint. Bireflectance is variable. The average of nine electron microprobe analyses gave Cu 35.33, Fe 1.18, Sn 58.18, and Sb 4.77, sum 99.46 wt%, corresponding to (Cu1.00Fe0.04)∑1.04 (Sn0.89Sb0.07)∑0.96. The powder pattern is close to those of natural Cu(Sn,Sb) and synthetic η-Cu6Sn5; it was indexed for a hexagonal cell, with a = 4.217(4) Å, c = 5.120(6) Å, and V = 78.85 Å3. For Z = 2, the calculated density is 7.6 g/cm3. The strongest lines in the pattern are at 2.970 (011), 2.112 (110), and 2.094 Å (012). The sorosite-bearing mineral assemblage apparently formed under low fO₂ and fS₂ conditions.Keywords:
Cassiterite
Placer deposit
Platinum group
Cleavage (geology)
Osmium-isotope ratios of individual PGM (platinum-group minerals) were determined lr sl/a using an ion microprobe. All samples except for one came from placers associated with Alpine- or Alaskan-type ultramafic intrusions. Most Alpine+ype samples are Os-Ir-Ru alloys, and most Alaskan-type samples are Pt-Fe alloys (isoferroplatinum or tetraferroplatinum), which contain Os-lr-Ru alloys and laurite/erlichmanite. Osmium-isotope measurements for the Pt-Fe alloys were carried out on those Os-bearing inclusions. The Os-isotope values are similar between cores and rims of PGM and among different inclusions of different phases within individual nuggets. No isotopic variations are observed in PGM that show profound chemical zoning. The-lack o^! isotopic heterogeneiry in individual nuggets precludes a low-temperature origin for rhe nuggets of PGM, 1876t71869, values of all samples show a narrow spread, ranging from 0.99 to 1.12, with most of the values between 1.00 and 1.06. These values fall within the range of l87Os/l86Os values of the mantle, suggesting essential derivation of platinum-group elements (PGE) from the mantle without a significant contribution of crustal Os. The grains of PGM were formed in intrusions' weathered, eroded, and concentrated in placers by mechanical processes. The Os-isotopic data are consistent with the occurrence of exsolulion lamellae of PGM, the inclusions of pristine unwealhered olivine, and the lack of foreign mineral inclusions, unrelated to ultramafic rocks, within the nuggets. Os-isotopic values for a placer nugget and PGM from chromitite in Urals also support the conclusion that the placer nugget was derived from the latter. The irregular shape and nonabraded surfaces of some nuggets may simply reflecr their durable nature and a short distance of transporl from the eroded ultramafic intrusions.
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Placer deposit
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Abstract Cassiterite mineralization occurs in both the rock and the alluvial system in the Mayo-Darlé area of northern Cameroon. This study focuses on the morphology, mineral inclusions, and composition of alluvial cassiterite derived from Bambol and Mayo Seni localities, where active alluvial mining by artisans constitutes the most important rural economic activity. The cassiterite grains were primarily analyzed by backscattered electron (BSE) images to investigate their morphological characteristics and mineral inclusions. The composition was examined through electron microprobe analysis (EMPA). The cassiterite grains have an irregular to sub-rounded morphology, indicating proximity to the source, although most of the cassiterite grains display evidence of mechanical transport and abrasion. EMPA results show mainly high SnO 2 content (93–103 wt. %), highlighting the predominance of cassiterite minerals in the humid tropical region. Among the Sn substituting elements, only Fe, Ta, and Mn were detected at very low concentrations (Fe = 0.02 to 0.3 FeO, Mn = 0 to 0.04 MnO, and Ta = 0 to 0.2 Ta 2 O 5 ) all in wt. % respectively, suggesting little variation in the alluvial cassiterite compositions. This high SnO 2 content indicates the purity of cassiterite in the area. Binary plots of compositional variation have similar trends, suggesting that cassiterite was derived from a single bedrock source, despite having a mixed signature of pegmatite- and hydrothermal-derived cassiterite. Mineral inclusions include quartz, hematite, and columbite group minerals (CGMs), which were similar in all the samples, suggesting a homogeneous source. The quartz inclusions highlight quartz veins associated with the mineralization and potential felsic plutonic bedrocks. The chemical signatures of the studied cassiterite grains are useful tools to explore the environment of an unknown primary source that can greatly help in mineral exploration in northern Cameroon.
Cassiterite
EMPA
Pegmatite
Columbite
Tourmaline
Topaz
Placer deposit
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Sorosite, ideally Cu(Sn5Sb), is a new mineral species from the Baimka gold-platinum- group mineral placer deposit, Chukotka, Russian Far East. It occurs as large subhedral to euhedral crystals (0.1-0.4 mm in length), hexagonal in cross section, minute crystals (≤ 15 μm, also hexagonal), and anhedral grains. Sorosite forms inclusions in Sb-bearing native tin, is often intergrown with stistaite (Sn1.12 - 1.13Sb0.87 - 0.88) and occurs with herzenbergite (SnS), native lead, and trace cassiterite. Sorosite is brittle with a microhardness VHN40;50 = 443.7 kg/mm2 (n = 3). No cleavage is observed. In reflected light, the large crystals are nearly white with a pinkish tint, whereas the microcrystals show a pronounced pinkish tint. Bireflectance is variable. The average of nine electron microprobe analyses gave Cu 35.33, Fe 1.18, Sn 58.18, and Sb 4.77, sum 99.46 wt%, corresponding to (Cu1.00Fe0.04)∑1.04 (Sn0.89Sb0.07)∑0.96. The powder pattern is close to those of natural Cu(Sn,Sb) and synthetic η-Cu6Sn5; it was indexed for a hexagonal cell, with a = 4.217(4) Å, c = 5.120(6) Å, and V = 78.85 Å3. For Z = 2, the calculated density is 7.6 g/cm3. The strongest lines in the pattern are at 2.970 (011), 2.112 (110), and 2.094 Å (012). The sorosite-bearing mineral assemblage apparently formed under low fO₂ and fS₂ conditions.
Cassiterite
Placer deposit
Platinum group
Cleavage (geology)
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Mineralogical investigation of platinum–group minerals (PGM) from the placer deposit in northwestern Hokkaido, Japan, was conducted at six rivers and two coasts covering an area of 70 km north–south and 30 km east–west: the Moshosanbetsu River (M), the Shosanbetsu River (S), the Ainusawa River (A), the Tomamae coast (T), the Obira coast (OC), the Kamikinenbetsusawa River (K), the Obirashibe River (OR), and the Numatapon River (N) from north to south. Details of the major PGM grain and the occurrence of small but diverse PGM inclusions were revealed in this study. Among diverse PGM inclusions, Cu3Pt mineral was discovered in PGM placer from the coast of Tomamae town, and it has been approved as a new mineral, tomamaeite, named after the type locality, by the International Mineralogical Association, the Commission on New Minerals, Nomenclature and Classification (IMA–CNMNC). Later, tomamaeite was also discovered in five localities. Tomamaeite occurs in Pt–Fe(Cu) alloys such as tulameenite, ferronickelplatinum, tetraferroplatinum, and hongshiite as an anhedral particle with a size of less than 20 µm. Tomamaeite is an opaque mineral and has metallic luster with a pale mist white color in reflected light. The hardness of tomamaeite has yet to be determined, although it is estimated to be ~ 3½ from comparison with compositionally related minerals and the calculated density is 12.4 g·cm−3 using the empirical formula and powder X–ray diffraction data. The empirical formula of tomamaeite calculated on the basis of 4 apfu is (Cu3.01Fe0.06Ni0.01)Σ3.08(Pt0.90Ru0.01Rh<0.01Pd<0.01Os<0.01Ir<0.01)Σ0.93, (Cu2.92Fe0.05Ni0.04)Σ3.01(Pt0.97Pd0.01Rh0.01)Σ0.99, (Cu2.86Sb0.13Fe0.03Ni0.02)Σ3.03(Pt0.92Ir0.02Pd0.01Os0.01)Σ0.97, (Cu2.71Sb0.19Fe0.02Ni0.02)Σ2.94(Pt1.01Ir0.05)Σ1.06, (Cu2.93Fe0.02)Σ2.94(Pt1.04Rh0.01)Σ1.06, and (Cu2.82Fe0.04Ni0.04)Σ2.90(Pt1.07Ir0.03Pd<0.01)Σ1.10 from the Tomamae coast, the Moshosanbetsu River, the Shosanbetsu River, the Ainusawa River, the Kamikinenbetsusawa River, and the Numatapon River, respectively. Crystal chemistry was investigated using tomamaeite from the Tomamae coast. Tomamaeite is cubic, Pm3m, with lattice parameters a = 3.683(2) Å and V = 49.97(7) Å3 (Z = 1) of Cu3Au–type structure, in which Pt occupies the position of origin, and Cu occupies the face–centered positions on a face–centered cubic lattice. PGM from northwestern Hokkaido probably have a mostly common origin and are characterized by depleted ultramafic rocks, and tomamaeite is a non–unique mineral that is formed during the universal post–magmatic process with alteration of such ultramafic rocks to serpentine.
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Pyroxene
Ultramafic rock
Placer deposit
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