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NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids
Jun Yan;  Ruizhong Hu;  Shen Liu;  Yangting Lin;  Jianchao Zhang;  Shanling Fu
2018
Source PublicationOre Geology Reviews
Volume92Pages:29-41
Abstract

Sulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As and S in pyrite from the deposit. Based on different textural pattern of pyrites revealed by back-scattered electron (BSE) images, they are divided into three types: Py-1 diagenetic pyrite without core-rim structure, Py-2 pyrite with an Au-free core and a rhythmically-zoned Au-bearing rim, Py-3 Au-bearing pyrite with rhythmic zoning across the entire grain. The element distributions and S isotope compositions of four paragenetic stages are recognized on the basis of textural observation. Py-1 grains and the Au-free homogeneous cores of zoned crystals were formed in Stage 1 while the Au-bearing rims of the zoned crystals with rhythmic zonation of As and Cu, and to a lesser degree Au, were formed in two superimposed stages: stage 2 formed the inner zone that is enriched in As alone; and stage 3 formed the outer zone that is enriched in both Au and As. Other sulfides such as realgar, cinnabar and stibnite are formed in the last stage. The relationship between Au and As distributions in pyrite rim is complicated, changing from coupled to decoupled at the nanoscale. Such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time, which in turn affect the modes of occurrence of As and Au. It is inferred that As mainly occurs in the crystal lattice replacing S whereas Au is mainly present as nanoparticles that were trapped in pyrite during crystal growth. The Au-bearing rims of the zoned pyrite crystals are characterized by highly variable delta S-34 values from 1.1 to 18.1 parts per thousand, which exceed the values of the Triassic calcareous host rocks (10-14 parts per thousand). In contrast, the delta S-34 values of the Au-free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12 parts per thousand, close to the values of pyrite crystals in the sedimentary country rocks. Our new analyses also reveals that the delta(34)5 values of the Au-bearing fluids generally increase during the formation of the deposit. The observed S isotope variations are consistent with mixing between a magmatic-related fluid with mantle-like delta S-34 value (similar to 0 parts per thousand) and a sedimentary or deep basin brine fluid with elevated delta S-34 value (>18 parts per thousand), with an increasing contribution from the latter with time. The notably varied values of delta(34)5 and the disseminations of Au and other trace elements such as As and Cu in pyrite crystals indicate that the process responsible for Au precipitation in this deposit occurred in an open hydro thermal system.

KeywordLannigou Au Deposit carlin-type Au Mineralization nanosims trace Elements pyrite invisible Gold sulfur Isotopes
Indexed BySCI
Language英语
Document Type期刊论文
Identifierhttp://ir.gyig.ac.cn/handle/42920512-1/8664
Collection矿床地球化学国家重点实验室
Affiliation1.State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
2.University of Chinese Academy of Sciences, Beijing 100039, China
3.State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, 229 Taibai Road, Xi'an 710069, China
4.Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Recommended Citation
GB/T 7714
Jun Yan;Ruizhong Hu;Shen Liu;Yangting Lin;Jianchao Zhang;Shanling Fu. NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids[J]. Ore Geology Reviews,2018,92:29-41.
APA Jun Yan;Ruizhong Hu;Shen Liu;Yangting Lin;Jianchao Zhang;Shanling Fu.(2018).NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids.Ore Geology Reviews,92,29-41.
MLA Jun Yan;Ruizhong Hu;Shen Liu;Yangting Lin;Jianchao Zhang;Shanling Fu."NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids".Ore Geology Reviews 92(2018):29-41.
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