Journal of Oceanology and Limnology - A variety of shell colors are one of the most fundamental characteristics of molluscs, which have importantly ecological and economic significance. The Pacific... 相似文献
Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1)replacement of earlier magnetite by pyrite and carbonaceous material;(2)alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate(mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits. 相似文献
The Sichuan–Yunnan–Guizhou (SYG) metallogenic province of southwest China is one of the most important Zn–Pb ore zones in China, with ~ 200 Mt Zn–Pb ores at mean grades of 10 wt.% Zn and 5 wt.% Pb. The source and mechanism of the regional Zn–Pb mineralization remain controversial despite many investigations that have been conducted. The Wusihe Zn–Pb deposit is a representative large-scale Zn–Pb deposit in the northern SYG, which mainly occurs in the Dengying Formation and yields Zn–Pb resources of ~ 3.7 Mt. In this paper, Zn and S isotopes, and Fe and Cd contents of sphalerite from the Wusihe deposit were investigated in an attempt to constrain the controls on Zn and S isotopic variations, the potential sources of ore-forming components, and the possible mineralization mechanisms. Both the δ66Zn and δ34S values in sphalerite from the Wusihe deposit increase systematically from the bottom to the top of the strata-bound orebodies. Such spatial evolution in δ66Zn and δ34S values of sphalerite can be attributed to isotopic Rayleigh fractionation during sphalerite precipitation with temperature variations. The strong correlations between the Zn–S isotopic compositions and Fe–Cd concentrations in sphalerite suggest that their variations were dominated by a similar mechanism. However, the Rayleigh fractionation mechanism cannot explain the spatial variations of Fe and Cd concentrations of sphalerite in this deposit. It is noted that the bottom and top sphalerites from the strata-bound orebodies document contrasting Zn and S isotopic compositions which correspond to the Zn and S isotopic characteristics of basement rocks and host rocks, respectively. Therefore, the mixing of two-source fluids with distinct Zn–S isotopic signatures was responsible for the spatial variations of Zn–S isotopic compositions of sphalerite from the Wusihe deposit. The fluids from basement rocks are characterized by relatively lighter Zn (~ 0.2 ‰) and S (~ 5 ‰) isotopic compositions while the fluids from host rocks are marked by relatively heavier Zn (~ 0.6 ‰) and S (~ 15 ‰) isotopic compositions.