Effect Of Gypsum Salt Rocks In The Mineralization Of Huize And Maoping Pb-Zn Deposits In Yunnan: Constraints From Sulfur Isotopic Compositions

The Huize and Maoping deposits,the famous high-grade Mississippi Valley-type Pb-Zn deposits in China,are located in the central south of the Sichuan-Yunnan-Guizhou Pb-Zn polymetallic ore cluster area in the southwestern margin of the Yangtze block.This study discussed effect of gypsum salt rocks on Pb-Zn mineralization of the Huize and Maoping deposits using sulfur isotopic compositions of sulfides,gypsum and carbonate-associated sulfate from the Huize and Maoping deposits.?³⁴S_V-CDT value of the Huize ore sulfides ranges from 11.0‰to20.0‰?averaging 14.7‰?.?³⁴S_V-CDT value of the carbonate-associated sulfate ranges from 10.4‰to 18.6‰?averaging 13.1‰?,slightly lower than the ore sulfides.?³⁴S_V-CDT value of the gypsum in the Carboniferous gupsum salt rocks ranges from12.9‰to 17.1‰?averaging 13.6‰?,which is consistent with that of carbonate-associated sulfate.?³⁴S_V-CDT value of the ore sulfides in the Maoping deposit is closely related to its occurrence layers.?³⁴S_V-CDT value of the ore sulfides in the Baizuo Formation?C₁b?ranges from 7.1‰to 17.5‰,with an average of 12.8‰,which is slightly lower than carbonate-associated sulfate and gypsum in Carboniferous carbonate strata.?³⁴S_V-CDT value of ore sulfides in Zaige Formation?D₃zg?ranges from 18.3‰to 22.7‰,with an average of 21.1‰.The results are unlikely with the ore sulfides in the Baizuo Formation?C₁b?or the Huize deposit.The?³⁴S_V-CDT value of the gypsum in the Zaige Formation?D₃zg?ranges from 21.9‰to25.9‰,with an average of 23.6‰,which is slightly higher than sulfides in the Zaige Formation?D₃zg?.By comparing the sulfur isotopic compositions of the sulfides,carbonate-associated sulfate and gupsum,we propose that the sulfur in the ore sulfides of Huize and Maoping Pb-Zn deposits mainly comes from the sulfate in the ore-bearing strata.In addition,sulfur in the ore sulfides of the Huize Pb-Zn deposit mainly came from Carboniferous gupsum salt layer,with only 10%of the sulfur from the underlying Zaige Formation gupsum salt layer;while sulfur in the Zaige Formation ore sulfides of Maoping Pb-Zn deposit derived from the Zaige Formation gypsum salt layer,sulfur in the Baizuo Formation ore body mainly came from the Baizuo Formation gypsum salt layer.That is,the gypsum was reduced in situ.Collectively,we divided the metallogenic process into two stages.At the first stage,gypsum reacted with the methane and/or other organic compositions forming hydrogen sulfide gas,which preserved in interlayer fissures or karst caves companied with large-scale dolomitization.At the second stage,ore-forming fluids containing Pb,Zn and other metals leached from the basement rocks and wall rocks mixed with the H₂S-rich fluids resulting in mineralization.