WANG Jing1, GAN Tian2,3*, YANG Jin-biao4, SHI Zeng-long5, FAN Yun-fei2,3, LUO Tai-yi3
(1. Construction Engineering Co. Ltd., Southwest Energy & Mine Group, Guiyang 550002, China;
2. School of the Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China;
3. The state Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry,Chinese Academy of Sciences, Guiyang 550081, China;
4. Yunnan Lancang Lead Mine Co. Ltd., Lancang 665601, China;
5. Yunnan ChiHong Zn & Ge Co. Ltd., Qujing 655011, China)
Abstract: Cu-Mo mineralization caused by granitic porphyry invading into basalt formation is one of distinctive metallogenesis located in Sanjiang metallogenic belt. The hydrothermal alternation system has been completely preserved in Laochang polymetallic deposit (Lancang Area, Yunnan Province, the southern end of Sanjiang belt, China), in which Carboniferous basaltic rocks have been invaded by deep concealed granitic porphyry. Based on determining the initial end-member rocks, element geochemistry research has been focused on desodiuming alteration in upper part of granitic porphyry and skarnization in basaltic wall rocks. Some results have been concluded. (1) The hydrothermal fluid in the upper part of granitic porphyry is enriched with Na-Ca-Si-Mn which is mostly from plagioclase decomposited alteration, characterized with extremely depleted Na and high K2O/Na2O rate (Desoudiuming). Till now no Na-enriched alteration has been found, we speculated that the element Na should be transferred into the runoff system. There is about 1%－2% SiO2 enriched in the upper part of granitic porphyry, however, there are obviously enriched Si and Ca in basaltic wall rock during skarnization（SiO2 average increment is about 4% to 5% and CaO average increment is about 5%).The characteristic Mn sourced from deep granite has most enriched 0.4－1.2 times in the upper part of granitic porphyry and basaltic wall rocks. (2) Elements Mo-Sn-Zn are mainly from granitic porphyry. Mo is enriched in the upper part of porphyry and adjacent basaltic wall rocks and extensively low ore-grade Mo mineralization has been confirmed, however, no Sn-Zn mineralization in contact zone of granitic porphyry has been found at present. Elements Ag-Pb-Bi-Cu mainly come from basalt. Cu is enriched in basaltic wall rocks and locally low ore-grade mineralization has been proved. Ag-Pb-Bi are enriched in the upper part of granitic porphyry and Ag-Bi-enriched galena veins have been explored in carbonate formation overlain upon Carboniferous basalt.（3）The rare-earth elements (REE) are totally depleted due to be activated and transported during the hydrothermal alternation in granite porphyry. Obviously differentiate has been observed in the element Eu (Eu: 0.85－1.32) during the process of activation. The REE is balance of gain and loss in skarnization of olivine basalt but obvious enrichment in skanization of tholeiite combining with slightly positive Eu anomaly.
Keywords: hydrothermal alteration system; desodiuming alteration; basalt skarnization; Himalayan granitic porphyry ; Laochang, Lancang,Yunnan
E-mail: gantian@mail.gyig.ac.cn
ACTA MINERALOGICA SINICA Vol. 36, No. 3, 2016, Page 329-342
