Ore Genesis Of Weibao Banded Skarn Lead-zinc Deposit Qimantagh Area, Xinjiang, China

In recent years, the Qimantagh area is becoming one of the most promising metallogenic belt in China, with numerous large to medium scale ore deposits discovered. The key metallogenetic event in this area, which is characteristic by huge reserves and various minerals, occurred in Triassic and is dominated by magmatic fluid induced deposits. However, hampered by the low research and prospecting degree, detailed mineralization processes of these deposits remain ambiguous, which has prevented the continuous success in mineral exploration in this area. In this thesis, we studied the Weibao lead-zinc district and reavealed its mineralization processes as well as the nature of ore-forming fluid, providing reference for the research and prospect of other deposits in this area.The Weibao lead-zinc district, composed by two deposits named the East Weibao deposit and the West Weibao deposit respectively, is located in the Qimantagh area, Eastern Kunlun Orogen. Although both controlled by skarn alternation and experienced similar mineralization processes, the East Weibao deposit is dominated by massive ores while the West Weibao deposit is characterized by banded ores. The ore-forming processes of both the two deposits can be divided into four stages including early skarn stage, late skarn stage, sulfide stage and carbonate stage. Three types fluid inclusions, i.e., pure CO2 fluid inclusion(PC-type), CO2-bearing fluid inclusion(C-type), and aqueous types(W-type), have been identified in quartz, calcite and sphalerite from different stages. Noteworthily, only sulfide stage of the East Weibao deposit contains carbonic fluid inclusions whereas only aqueous fluid inclusions were observed in sulfide stage of the West Weibao deposit. The CO2-rich and aqueous type fluid inclusions in sulfide stage of the East Weibao deposit were homogenized at temperatures between 263 oC and 424 oC, concentrating at 360-400 oC, with salinities ranging between 3.2 wt.% Na Cl eqv. and 13.6 wt.% Na Cl eqv.; the W-type fluid inclusions in sulfide stage of the West Weibao deposit were homogenized at temperatures between 228 oC and 381 oC, concentrating at 280-340 oC, with salinities between 1.6 wt.% Na Cl eqv. and 9.0 wt.% Na Cl eqv.; and the aqueous type fluid inclusions in carbonate stage in both deposits were homogenized at temperatures between 115 oC and 336 oC, concentrating at 200-240 oC, with salinities between 0.2 wt.% Na Cl eqv. and 5.9 wt.% Na Cl eqv.. These data illustrate a decreasing trend of both temperatures and salinities and medium-high temperatures and salinities in ore-forming fluids at both deposits, indicating a likely magmatic-hydrothermal origin. The ore-forming fluid in sulfide stage at the East Weibao deposit yielded calculated δ18OH2O and δ18D values of 4.2–5.6 ‰ and-88–-83 ‰, respectively. The results are 8.8–10.8 ‰,-99–-92 ‰ for the sulfide stage at the West Weibao deposit and-1.0–-0.2 ‰,-50–-45‰ for carbonate stage. The fluid inclusion and hydrogen, oxygen isotope study on the two deposits in the Weibao lead-zinc district suggest that they both have magmatic origin but mineralized by different mechanisms. Mineralization at the East Weibao deposit may be caused by fluid immiscibility and mixing, while at the West Weibao deposit mineralization may result from water-rock reactions between magmatic fluid and impure carbonate wall rocks. The lead isotopic ratios of sulfide samples from the Weibao lead-zinc district range between 18.259 and 18.336 for 206Pb/204 Pb, 15.580 and 15.659 for 207Pb/204 Pb, 38.007 and 38.253 for 208Pb/204 Pb, respectively, and the corresponding sulfur isotopic values rang between-2.2 ‰ and 3.6 ‰. The lead and sulfur isotopic compositions demonstrate that the ore-forming materials were derived from the mixing between wall rocks and the Triassic granitoid by metasomatism, with the minor contribution of mantle materials. Hence, we conclude that the Weibao lead-zinc district as a united magmatic hydrothermal fluid system associated with the Triassic magmatism that widely distributes in the Qimantagh area.