Gold Enrichment and the Au–Te Association in the Huangtan Au–Cu–Zn Volcanogenic Massive Sulfide Deposit, Kalatag, East Tianshan, China: An in-situ LA–ICP–MS Analysis

Abstract

Abstract Huangtan Au–Cu–Zn is an auriferous VMS deposit hosted in tuff breccia, and tuff of Silurian age in the Kalatag area that located in the northern part of East Tianshan. Mineralization can be divided into two principal ore facies: massive, semimassive ore and stockwork ore. Pyrite, chalcopyrite, and sphalerite, as the predominant sulfide minerals and Au–bearing minerals, were investigated using a combination of ore microscopy, EMPA, SEM–EDS, and in situ LA–ICP–MS. There is no clear systematic variation in the trace element distribution with different types of pyrite, chalcopyrite, and sphalerite in the massive ore, stockwork ore, and hydrothermal alteration zone. Combined with mineralogical characteristics, this deposit is considered to be the product of the same ore-forming fluid and belongs to the VMS metallogenic system. Gold in the Huangtan deposit is present in three main mineralogical forms: auriferous tellurides, “invisible” gold, and native gold. Tellurides identified in the Huangtan deposit include: calaverite, sylvanite, petzite, native tellurium, hessite, altaite, and tellurobismuthite. LA–ICP–MS depth profiles, and mapping imaging for Au, Ag, and Te suggest that the invisible gold in pyrite, chalcopyrite, and sphalerite are micro- to nanoscale inclusions of Au–Ag–Te assemblages. Native gold contains smaller amounts of Ag, Bi, Te, and Se. The concentrations of trace elements Au, Te, Ag, Bi, and Se in pyrite, chalcopyrite, and sphalerite are strongly correlated, indicating that the ore-forming fluid was likely of magmatic origin. In addition, the sulfur isotope compositions (–3.3‰ to 2.3‰) of different types of major sulfides have a narrow range, indicating a homogeneous sulfur source, and show that sulfur sources were mainly derived from magmatic sulfur. The mineral assemblages reveal that Au–Te precipitated under variable redox conditions with log ƒTe2 being less than −8 in the massive ore, and log ƒTe2 being greater than −12.5 in the stockwork ore. The formation of tellurides is sensitive to the temperature of the mineralization system. With the decreasing temperature, the auriferous tellurides gradually precipitated and formed the Huangtan Au–Cu–Zn deposit with an auriferous telluride ore body.