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Lode‐gold mineralization in the Bétaré Oya gold district is related to a series of quartz–sulphide veins that define a steeply dipping NNE–SSW‐trending brittle–ductile shear zone. The veins transect metasedimentary sequences in the vicinity of small granitic intrusions. Quartz veins range from barren (massive quartz) to mineralized with textures that vary from foliated, sheared, vuggy, fractured, and sugary to brecciated with inclusions of altered wall rock. They contain gold, pyrite, and galena in addition to chalcopyrite and both hypogene and supergene haematite and covellite. Parameters that consistently define primary gold mineralization in the area include silicification, sulphidation, sericitization, K‐feldspar alteration, haematitization, and carbonatization. Gold grains recovered from heavy mineral concentrate and grains that occur as inclusions in pyrite were characterized by microchemical methods. The gold grains are zoned and exhibit a simple internal structure of partly deformed and leached rims and high‐purity intragranular veinlets. Gold is alloyed with Ag; gold fineness varies between 859 and 877 in the core and from 958 to 997 in the leached rims. Inclusions of gold in pyrite cluster between 875 and 900. Pyrite has up to 0.59 wt% Au, and other trace elements occur in low quantities but for Pb (0.13 wt%), Ag (1.36 wt%), and Sb (1.63 wt%). The bulk trace element signature of the veins is characterized by Au, Ag, As, Bi, Ba, Cr, Cu, Mn, Pb, Sb, Sr, V, W, Zn, and Zr. This depicts a geochemical association of Au ± Cu ± Bi ± As ± Pb. The occurrence of Au as well as elevated Pb and Zn could suggest a granitic source for the ore‐bearing fluid. The auriferous quartz veins are characterized by a widespread in δ34S from 2.8 to 14.9‰ pointing to multiple sources of sulphur in the system, perhaps a mixture of sulphur from the metasedimentary and the granitic rocks. [ABSTRACT FROM AUTHOR]

The Batouri gold mining area in southeastern Cameroon is part of the Adamawa–Yadé Domain of the Central African Fold Belt (Pan-African). It is underlain by a variety of granitic rocks, including alkali-feldspar granite, syeno-monzogranite, granodiorite, and tonalite. Geochemical data suggest that these rocks formed by differentiation of I-type tonalitic magma under oxidizing conditions in a continental volcanic arc setting. U–Pb dating of zircons from gold-associated monzogranite-granodiorite at Kambélé gave concordant ages of 619 ± 2 and 624 ± 2 Ma, while Ar–Ar dating of alkali-feldspar granite yielded a non-plateau maximum age of 640–620 Ma. These ages imply that the Batouri granitoids were emplaced during the collision of the West African Craton and the Congo Craton. The geochemical characteristics of the Batouri granitoids as well as their oxidized state (magnetite series) are typical of gold-associated felsic rocks in subduction settings elsewhere. The similarities in age, composition, and geochemical affinities of these granitoids with those reported from other localities in the Adamawa–Yadé Domain reinforce the earlier assumption that the granitic rocks of this domain represent parts of a regional-scale batholith, with commonly small-scale, high-grade auriferous quartz veins in structurally favourable sites. The spatial and temporal association of gold mineralization and the Batouri granitoids may suggest potential for regional-scale, high-tonnage, granite-related gold ore. [ABSTRACT FROM AUTHOR]

The Neoproterozoic granitic rare-metal pegmatites of the Gatumba mining district in western Rwanda have very low base-metal and sulfide content, and are very low in arsenic or other hazardous metals. However, their hydrothermal halos display slight enrichment in thallium at a meter scale, while arsenic may be enriched in associated tin-bearing hydrothermal systems in distant country rock. Columbite–cassiterite concentrates have a few hundred ppm of As, Bi, U and Th which, when calculated back to the pegmatite bulk rock, correspond to a composition near average continental crust. Pegmatite tailings material can provide a fertile substratum for agriculture because these rocks have no deleterious elements, buffer soil pH near neutral conditions, and also are slightly enriched in potassium and phosphorus compared to most soil cover in Rwanda. [ABSTRACT FROM AUTHOR]

Bulk chemical analyses for Pt and Pd in marine Fe–Mn nodules and crusts from different provenances are presented, together with a wide range of elements. Platinum contents vary from 70–328 ppb, whereas Pd contents extend from 0.6–4.7 ppb only. Bromine and Pb show strong positive correlations with Pt. Lead is remarkably enriched in Fe–Mn precipitates over seawater, but Br is a conservative-type element in seawater and shows no enrichment in Fe–Mn precipitates. Hence, the Pt–Br–Pb element association combines two elements, Br and Pb, of extremely contrasting enrichment factors in Fe–Mn precipitates. [ABSTRACT FROM AUTHOR]

Quartz-hosted melt inclusions from latite dykes of the Eocene El Salvador copper porphyry system in northern Chile display wide ranges in both boron concentration (15–155 p.p.m. B) and isotope composition (δ11B −7 to +12‰; n = 10), likely reflecting slab-derived fluid input from seawater-altered oceanic crust. In contrast, the major Miocene tin-silver and tin porphyry systems in the Bolivian back-arc region (Cerro Rico de Potosi, Chorolque, Llallagua) have distinctly different melt inclusion compositions with δ11B of −11.4 ± 2.7‰ ( n = 10), and magmatic boron enrichment up to several hundred p.p.m. B. The `seawater' signature in the El Salvador melt inclusions explains the oxidized mineral assemblage of the copper porphyry system, as opposed to the more reduced nature of the Bolivian tin porphyry systems, which reflect intracrustal melting of pelitic rocks. [ABSTRACT FROM AUTHOR]

About 85% of all historically mined tin of about 27 million tonnes Sn is from a few tin ore provinces within larger granite belts. These are, in decreasing importance, Southeast Asia (Indonesia, Malaysia, Thailand, Myanmar), South China, the Central Andes (Bolivia, southern Peru) and Cornwall, UK. Primary tin ore deposits are part of magmatic-hydrothermal systems invariably related to late granite phases (tin granites, pegmatites, tin porphyries), and may become dispersed by exogenic processes and then eventually form placer deposits within a few km from their primary source, due to the density of cassiterite, its hardness and chemical stability. Alluvial placer deposits were usually the starting point for tin mining, and have provided at least half of all tin mined. The small-volume and late granite phases in spatial, temporal and chemical relationship to tin ore deposits are highly fractionated. Systematic element distribution patterns in these granite phases and their associated much larger multiphase granite systems suggest fractional crystallization as the main petrogenetic process controlling magmatic evolution and magmatic tin enrichment. Oxidation state controls the bulk tin distribution coefficient, with low oxidation state favoring incompatible behavior of divalent tin. Low oxidation state is also mineralogically expressed by accessory ilmenite (FeO TiO 2) as opposed to accessory magnetite (FeO Fe 2 O 3) in more oxidized melt systems. This difference in the accessory mineralogy and hence metallogenic potential (tin-bearing ilmenite-series versus barren magnetite-series granites), can be easily detected in the field by a hand-held magnetic susceptibility meter. The hydrothermal system is a continuation of the magmatic evolution trend and necessary consequence of the crystallization of a hydrous melt. The exsolved highly saline aqueous fluid phase, enriched in boron and/or fluorine plus a wide metal spectrum, can be accomodated and stored by the intergranular space in crystallized melt portions, or accumulate in larger physical domains, accompanied by focused release of mechanical energy (brecciation, vein formation), dependent on emplacement depth (pressure). The hydrothermal mobility of tin is largely as Sn2+-chloride complexes; the precipitation of tin as cassiterite involves oxidation. Tin typically characterizes the inner high-temperature part of much larger km-sized zoned magmatic-hydrothermal systems with the chemical signature Sn-W-Cu-As-Bi in the inner part (greisen, vein/stockwork/breccia systems, skarn) and a broader halo with vein- or replacement-style Pb-Zn-Ag-Sb-Au-U mineralization of lower temperature. This zoning pattern may also occur telescoped on each other. Active continental margins are the favorable site for both copper (−gold) and tin (−tungsten) systems. However, the narrowly segmented metal endowment and the episodic nature of ore formation suggest additional controls. These are the build-up of a subduction-derived metal and fluid inventory in the lower continental crust by flat-slab subduction (very little magmatism) for copper‑gold in the main arc, followed by large-scale intracrustal melting during mantle upwelling in the back arc for tin (chemically reduced reservoir rocks) and/or tungsten mineralization (less sensitive to oxidation state). [Display omitted] • Tin granites display advanced degree of fractionation • Tin granites are of ilmenite series (reduced), irrespective of S-, I-, or A-type affinity • Hydrothermal tin solubility is optimal under reducing and highly saline conditions • Hydrothermal tin ore formation requires oxidation, fluid mixing, cooling [ABSTRACT FROM AUTHOR]

We present Mo isotope data for molybdenite from the Ekomédion U-Mo prospect, SW Cameroon, a Late Neoproterozoic granite-pegmatite-quartz vein system. Disseminated and veinlet-controlled molybdenite in granite and pegmatitic pods yields a narrow range of δ98Mo values from - 0.06 to + 0.24 ‰, with two overlapping populations of + 0.03 ± 0.07 ‰ (n = 4) in granite, and slightly heavier of + 0.11 ± 0.10 ‰ (n = 5) in pegmatite. By contrast, molybdenite from a quartz-muscovite vein has an isotopically heavy δ98Mo value of + 1.61 ‰. We interpret this trend from granite through pegmatite to vein system towards isotopically heavy Mo to reflect the fractionation of an evolving magmatic-hydrothermal system. Furthermore, the LREE-enriched bulk-rock patterns with largely negative Eu anomalies and the overall enrichment of HREE in zircon indicate plagioclase fractionation as the dominant petrogenetic process during melt evolution. Furthermore, the presence of accessory ilmenite indicates relatively reducing conditions of the melt system, unfavorable for significant Mo accumulation. Therefore, the Ekomédion granite system seems to have limited economic potential for molybdenum despite the advanced degree of magmatic evolution. [ABSTRACT FROM AUTHOR]

The banded iron formation (BIF) in the Gebel El Hadid area is part of the Late Neoproterozoic island-arc/ophiolitic assemblage of the central Eastern Desert of Egypt, where it alternates concordantly with low-grade metavolcaniclastics. The BIF units are mainly of oxide facies consisting of iron oxide mesobands with intercalations of quartz–carbonate ± chlorite ± magnetite mesobands in the form of layers and pods. Geochemically, the Gebel El Hadid BIF is characterized by heavy REE-enriched NASC-normalized patterns, rarely with a weak positive Eu anomaly. The Neoproterozoic age of the Egyptian BIF suggests that they are of Rapitan type, but their size, petrological and geochemical characteristics suggest that they are of Algoma type having formed before the final collision between major fragments of East and West Gondwana. The nature and composition of the BIF and associated metavolcaniclastics indicate their formation as a result of submarine hydrothermal activity concomitant with arc volcanism. The Gebel El Hadid BIF units were deposited in pulses during periods of quiescent arc activity at ca. 717 ± 8 Ma (U–Pb age on volcaniclastic zircon). Submarine diagenesis under suboxic conditions produced an early generation of magnetite, hematite and quartz, whereas regional metamorphism led to the formation of coarse-grained and porphyroblastic magnetite and quartz. Post-metamorphic oxidation led to martitization of magnetite, and formation of hematite and specularite. [ABSTRACT FROM AUTHOR]

Carbonaceous calcitic chalk from a 50-m stratigraphic section of the Maastrichtian-Danian Muwaqqar Chalk Marl (MCM) Formation, Jordan, has elevated concentrations of biophile and/or redox-sensitive trace metals (Mo, Ni, V, U, Cr, Cd, Ag, Se, and P) which indicate enhanced paleo-bioproductivity, biodegradation and remineralization under reducing conditions. Very low concentrations in Mn and Ba suggest a relatively open system for components mobile under reducing conditions. The last 800,000 years to the K/Pg boundary are not exposed in Jordan, but the stratigraphic 20-m-interval below and above the hiatus of the K/Pg transition (n = 8) with 2.6 ± 1.8 wt% organic C is particularly metal-enriched with average bulk-rock contents of 132 ppm Mo, 177 ppm Ni, 363 ppm V, 576 ppm Zn, 39 ppm Se, 1.4 ppm Ag, 106 ppm Cd, 474 ppm Cr. These concentrations are dominantly of authigenous origin, when normalized to PAAS, i.e. 100 % Mo, 100% Ag, 100% Cd, 96% Cr, 95% Ni, 95% Zn, 80% V authigenous, and testify to ≥90% of biodegradation of planktonic debris by anaerobic bacterial activity at or near the seafloor. The depositional environment is euxinic, and Mo/TOC ratios from <10 to around 100 (as well as analogous trends for Ni/TOC and Cr/TOC) indicate an evolution from initially restricted hydrographic conditions to unrestricted open-sea conditions towards the K/Pg transition. The common paleoenvironmental proxies for black shale such as V, V/(V + Ni) and V/Cr ratios, indicate oxic depositional conditions for the studied chalk, which are misleading because the low illite content in the calcareous ooze does not allow sufficient retention of V in this chalk. REE patterns identify a seawater and a clastic component to about equal amounts on average, with authigenous ΣREE of 23 ± 19 ppm (n = 20). The negative Ce anomaly of the authigenous component is −0.6 ± 0.2 (log PAAS normalized), compared to recent seawater with −1.1. The geochemical composition of the carbonaceous calcitic chalk sequence is an expression of the general Cretaceous-Paleogene upwelling regime on the southern passive margin of the Neo-Tethys Ocean in the Cretaceous-Palaeogene (K-Pg) greenhouse environment. • Carbonaceous calcitic chalk was deposited in a shelf setting under reducing conditions. • The low abundance of Al 2 O 3 , Th, Zr, REE, indicates a subdued terrigenous input. • The K/Pg boundary has particularly elevated redox-sensitive and biophile trace element contents. • Elevated redox-sensitive and biophile metal contents indicate high bioproductivity and biodegradation. [ABSTRACT FROM AUTHOR]