The Relationships Between Calcites And Metallogenic Process And Prospecting Significance In Zhesang Carlin-Like Gold Deposit,Funing,Southeastern Yunnan Province

There are a large number of Carlin-like gold deposits in the"Golden Triangle"of Yunnan,Guizhou and Guangxi,and the Zhesang gold deposit in Southeast Yunnan is an important part of it.In recent years,much progress has been made in the study of the deposit,but there is still much controversy on the source of ore-forming fluid,which restricts the further study of the deposit.Calcite is one of the most common hydrothermal gangue minerals.Therefore,this paper selects calcite,a hydrothermal gangue mineral,as the research object.By means of calcite trace elements,fluid inclusions,Nd,C,O isotopes and other geochemical means,the source of ore-forming fluid,the relationship between the formation of calcite and gold precipitation,and the exploration by using calcite geochemical parameters are studied in detail.The main achievements are as follows:?1?The ore-stage calcite is enriched in middle rare earth elements?MREE?relative to light rare earth elements?LREE?and heavy rare earth elements?HREE??MREE/LREE=1.11–1.61,MREE/HREE=6.12–8.22?,whereas post-ore calcite exhibit an enrichment in LREE?LREE/HREE=4.39–14.93,MREE/LREE=0.35–0.71?.The Fe contents of the ore-stage calcite?4690–6300?g/g?are significantly higher than those of post-ore calcite?2030–2730?g/g?.Ore-stage calcite?11.03–12.49‰?has significantly lower?¹⁸O_V-SMOWvalues than post-ore calcite?16.48–17.14‰?.Sr/Ba ratio of two stage of calcites are greater than 1.The most fluid inclusions uniform temperature of calcite in the ore-stage?185.7–234.1°C?is higher than those of post-ore calcite?141.2–189.5°C?.The fluid inclusions salinity of calcite in the ore-stage?11.7–22.0%?is higher than those of post-ore calcite?4.3–9.4%?.The density of calcite fluid inclusions in the ore-stage?0.90-1.05 g/cm³?is similar to that post-ore?0.90-1.00 g/cm³?.?2?The study of fluid inclusions shows that the ore-forming fluid is a low-temperature,medium-salinity and low-density fluid.Fluid of post-ore is a low-temperature,low-salinity and low-density fluid.Nd isotopic study shows that the ore-forming fluid comes from low Sm/Nd continental crust.C-O isotope studies have shown that the C and O isotopes of the two stage fluid mainly come from the interaction between atmospheric precipitation and marine carbonate rocks,and the ore-forming fluids were contaminated with a small amount of alkaline magmatic fluid.Studies on REE elements show that the two stage calcites were both formed by hydrothermal fluids,however,these hydrothermal fluids have distinctly different sources.The REE of the ore-forming fluids mainly come from the host rock,some of the REE may come from the basic magma fluid,and the REE of the post-ore fluid come from the host rock.The study of other trace elements shows that the ore-forming fluid is rich in Mo,Sn,Ni,Cu and other high-temperature ore-forming elements,Pb,Sb and other low-temperature ore-forming elements,and the ore-forming materials may come from volcanic rocks and marine sediments.Based on the above study,it is considered that the ore-forming fluid of Zhesang gold deposit is formed by the surrounding rock drenched by atmospheric precipitation,and contains a small amount of basic magmatic fluid,which has the characteristics of medium low temperature,medium salinity and low density.The fluid after mineralization period comes from the dissolution of marine carbonate rocks by atmospheric precipitation,which is characterized by low temperature,low salinity and low density.The ore-forming fluid of the Zhesang gold deposit is related to the intrusion of the diabase exposed in the deposit.The basic magmatic activity in the Indosinian period also provided certain ore-forming materials and heat for gold mineralization.?3?Calcite is an important gangue mineral in Zhesang gold deposit,which plays an important role in the process of gold mineralization.The decarbonization of the surrounding rock provides the material basis for the formation of calcite,as well as the iron required for the sulfurization in the process of gold precipitation.Calcite and gold mineralization are formed at the same time,both of them consume the Fe element in the fluid,forming calcite and gold bearing sulfide respectively.The formation of calcite may change the acidity and basicity of ore-forming fluid and promote the deposition of gold.?4?There calcites with MREE/LREE ratio greater than 0.92,MREE/HREE ratio greater than 5.69,Fe content greater than 3827?g/g,?¹⁸O_V-SMOWvalue less than14.40‰,Sr content less than 704?g/g,Ba content less than 3.7?g/g,salinity greater than 10.6%,and uniform temperature greater than 193.6?,represent ore-stage calcites and are important prospecting clues.Calcite is an important gangue mineral of Carlin-like gold deposits in Yunnan Guizhou Guangxi area.The study of calcite geochemical characteristics(including REE,Fe element content and?¹⁸O_V-SMOWvalue)can provide an important basis for the exploration of Carlin-like gold deposits in Yunnan Guizhou and Guangxi area.