Paleozoic Gold Deposits Research Articles

Sericite 40Ar/39Ar dating and S-Pb isotope composition of the Kanggur gold deposit: Implications for metallogenesis of late Paleozoic gold deposits in the Tianshan, central Asian Orogenic Belt

The Tianshan is one of the largest gold provinces on Earth and hosts several giant gold deposits, while most giant gold deposits are distributed in the western and central segments of the Tianshan (i.e., the Western Tianshan) but not in Chinese Tianshan. Thus, the differences for metallogenesis of gold deposits between the Western and Chinese Tianshan attract intensive interest but remain ambiguous. Here we present sericite 40Ar/39Ar ages and S–Pb isotope compositions of pyrite from the Kanggur gold deposit, the largest shear zone-related gold deposit in the Chinese Tianshan. By integrating new sericite 40Ar/39Ar plateau ages (262.71 ± 2.95 Ma and 263.40 ± 2.94 Ma) with previous geochronological results, three peaks in gold mineralization are identified for the entire Tianshan: an early peak at ca. 330 Ma during which time subduction–accretion-related porphyry-type and orogenic gold deposits formed, a middle peak at ca. 290 Ma during which time post-collisional magmatism-related orogenic gold deposits formed in a collisional compressional to post-collisional extensional environment, and a late peak at ca. 260 Ma during which time strike–slip shear zone-related orogenic gold deposits formed in a post-collisional extensional environment. The sulfur (δ34SV-CDT of −1.0 to +2.5‰ for pyrite from ores and −1.9 to +2.6‰ for pyrite from wall rocks) and lead (18.199–18.231 for 206Pb/204Pb, 15.585–15.624 for 207Pb/204Pb, 38.104–38.229 for 208Pb/204Pb for pyrite from ores, and 18.176–18.244 for 206Pb/204Pb, 15.583–15.611 for 207Pb/204Pb, 38.090–38.205 for 208Pb/204Pb for pyrite from wall rocks) isotope compositions of pyrite indicate that the metals in gold deposits throughout the Tianshan were sourced from different reservoirs. In the Western Tianshan, the ore-forming metals for the deposits southwest of longitude 70°E were mainly sourced from upper crustal reservoirs, whereas those east of longitude 70°E were mainly sourced from lower crustal reservoirs. In the Chinese Tianshan, however, the ore-forming metals were dominantly sourced from lower crustal and/or mantle reservoirs. These different reservoirs were likely responsible for the distinct characteristics of the gold deposits located in the Western and Chinese Tianshan.

Physicochemical Parameters and Geochemical Features of Fluids of Paleozoic Gold Deposits

Physicochemical Parameters and Geochemical Features of Fluids of Paleozoic Gold Deposits

THE BALKAN MOUNTAINS PALEOZOIC GOLD DEPOSITS

A number of Paleozoic gold deposits are situated in the Hercynian terrains of the Balkan Mountain. On Bulgarian territory Govezhda and Svishti Plaz deposits are the most important ones. Neresnitza, Blagoev-Ka nen and Osanitza deposits are located in the Serbian part of the Balkan Mountain. All these deposits are hosted in the Pre-Alpine basement of the Balkanide zone. The orehosting structures are veins, lenses and mineralized fissures related to tension and shear faults. The structural characteristics of the ores are an evidence for tectonic control and tectonic activity during the ore deposition. All stages of ore deposition were accompanied by strong fracturing of already deposited minerals and subsequent precipitation of next portion. The economically important mineral in all these deposits is the native gold, with variable Ag contents. In the two Bulgarian deposits the main ore minerals are arsenopyrite and pyrite. Arsenopyrite is not reported for Serbian deposits, but scheelite is a main mineral there instead. Based on mineral associations, three possible genetic concepts of Au deposition could be expressed. 1) The gold is genetically associated with arsenopyrite and pyrite from stage 1 (Fe-As- Au+W). It is primarily deposited as invisible gold in these minerals. During the next stage of sulfide deposition driven by induced heating, it is remobilized and redeposited in cracks, formed during the cataclastic events of this stage. 2) The gold is genetically connected to the stage 2 (Pb-Zn-Cu-Ag- Au). 3) Dual generation of gold related to both stages 1 and 2. All Balkan Paleozoic gold deposits show lots of similarities to mesothermal gold deposits in shear zones in Archaean greenschists terrains in Canada, Western Australia and Africa, as well as to Hercynian gold deposits in France and Portugal. The similarity especially concerns their connection to granodiohtic magmatism, the mineral parageneses and the gold occurrence and its associations. Despite that the mining in the Balkan gold deposits is already closed, they still have nonexplored and non-operated reserves

A comparison of alteration assemblages associated with Archean gold deposits in Western Australia and Paleozoic gold deposits in the southeast United States: Discussion

Ririe states that the purpose of his comparison of the mineralogy and chemistry of gold deposits from Western Australia (Sons of Gwalia and Mount Celia) and the Carolina slate belt (Haile and Brewer) is illustrate that alteration in these two terranes is the result of similar processes that were also responsible for the introduction of gold into the altered (p. 1561). The alteration assemblages contain highalumina minerals such as andalusite, kyanite, pyrophyllite, kaolinite, and sericite, plus local alunite. Ririe interprets these rocks as having ... been altered by acid hydrothermal solutions prior to regional (p. 1561) based upon relations [that] indicate that the rocks had their alteration composition by the time the suite of aluminosilicate minerals was forming (p. 1574) and the absence of documented low-pH regional metamorphic fluids capable of producing alunite plus a suite of high-alumina minerals such as andalusite-pyrophyllite (p. 1574). He concludes that the best analogs for these gold deposits are acid-sulphate epigenetic gold deposits such as Goldfield, Nevada, and modern geothermal systems. The important question to be asked is, Does the presented evidence convincingly support the interpretation? In this writer's opinion, the presented evidence does not positively answer this question. ~easons why the two principal arguments proposed above by Ririe inadequately support his interpretation follow below. The textural evidence consists of photomicrographs of randomly oriented andalusite porphyroblasts, fractured and rotated andalusite crystals, and folded quartz-pyrophyllite + pyrite banding in the Western Australia deposits (Fig. 3, p. 1564), randomly oriented andalusite porphyroblasts at Brewer, and deformed and altered argillite at Haile (Fig. 7, p. 1568). It is reasonable to suggest that the high-alumina assemblages reflect metamorphism of a previously altered and 1 aluminous rock. But that is all that it proves; the products of hydrothermal alteration have been metamorphosed! However, I the critical questions is the timing of hydrothermal alteration relative to metamorphism and regional deformation? and What is the metamorphic and deformation history of the surrounding country rocks? are not addressed. ree ens chi st facies regional metamorphism is implied for Western Australia or stated (Carolina slate belt, p. 1563) with only one period of deformation and metamomhism imolied. ow ever. more than one period of deformationkd metahorphism occurred in both the Norsemen-Wiluna greenstone belt (Archibald et al. 1978; Bickle and Archibald 1984) and the Carolina slate belt (Williams and Hatcher 1983).

A comparison of alteration assemblages associated with Archean gold deposits in Western Australia and Paleozoic gold deposits in the southeast United States: Reply

A comparison of high-alumina mineral assemblages spatially associated with the Haile and Brewer gold deposits in the Paleozoic Carolina slate belt (CSB) of the southeast United States and the Sons ...

A comparison of alteration assemblages associated with Archean gold deposits in Western Australia and Paleozoic gold deposits in the southeast United States

A comparison of high-alumina mineral assemblages spatially associated with the Haile and Brewer gold deposits in the Paleozoic Carolina slate belt (CSB) of the southeast United States and the Sons of Gwalia and Mount Celia gold deposits in the Archean Norseman–Wiluna greenstone belt (NWGB) in Western Australia suggests a similar hydrothermal origin and subsequent metamorphic and deformational history. A common hydrothermal origin is supported by the striking similarity in whole-rock chemistry, even though there were probably significant variations in original unaltered protoliths. An analysis of rocks from each of the deposits that contain high-alumina minerals demonstrates that the protoliths were leached of alkalis with respect to aluminum and have a ratio of Al2O3/Na2O + CaO + K2O greater than three. Although the rocks contain abundant high-alumina minerals, the aluminum content in these rocks is not unusually high, and it does not appear that there has been any significant transport of aluminum either into or out of the rocks that were altered.The most common high-alumina minerals found in rocks affected by the feldspar destructive alteration event include andalusite, kyanite, pyrophyllite, kaolinite, and sericite. Other minerals present in variable amounts include diaspore, chloritoid, alunite, natroalunite, paragonite, and topaz. It is possible that some of these minerals formed during the early hydrothermal alteration event and were recrystallized during metamorphism. Regardless of when the high-alumina minerals formed, textural relations suggest that the rocks had been hydrothermally altered by the time the metamorphic minerals formed. A comparison of alteration from the deposits studied in the CSB and the NWGB suggests there are many similarities to acid-sulfate alteration associated with geothermal areas, such as Yellowstone Park, Wyoming, and with acid-sulfate gold deposits, such as Goldfield, Nevada. Thus, it is possible that the protolith of the metamorphosed rocks in the CSB and NWGB contained an alteration assemblage that included alunite, pyrophyllite, and kaolinite.A generalized paragenetic sequence determined from petrographic and field observations, beginning with regional metamorphism, follows: (i) formation of andalusite, kyanite, chloritoid, and topaz during prograde metamorphism, depending on whole rock chemistry, (ii) formation of pyrophyllite and quartz-rich pods during silicification of aluminosilicate-bearing rocks, (iii) bedding parallel schistosity and fracturing produced by a deformational event, (iv) fractures filled by quartz, sericite, pyrophyllite, or calcite, (v) folding of early layering in the rocks to form a crenulation cleavage accompanied by introduction of quartz veins at high angles to foliation; and (vi) retrograde metamorphism of andalusite–kyanite-pyrophyllite to produce an assemblage of kaolinite ± diaspore.The spatial association of the acid-sulfate alteration with gold mineralization, together with comparison of analogous alteration associated with younger unmetamorphosed acid-sulfate gold deposits, suggests that at least some of the gold was introduced during the early premetamorphic alteration event. The present location of gold in each deposit is a result of local changes brought about by later metamorphic and deformational events.

Recent developments in the study of Archean gold deposits Développements récents dans l'étude des gisements d'or archéens

Recent developments in the study of Archean gold deposits Développements récents dans l'étude des gisements d'or archéens