Ilvaite as a thermodynamic recorder of multistage retrograde alteration in large Galinge skarn Fe deposit, western China  

黑柱石-青海尕林格矽卡岩铁矿多期退化蚀变记录（英文）

作　　者：YU Miao Jeffrey MDICK MAO Jing-wen FENG Cheng-you LI Bin LU An-huai ZHU Yong-feng LAI Jian-qing 于淼;Jeffrey MDICK;毛景文;丰成友;李斌;鲁安怀;朱永峰;赖健清(Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Ministry of Education),Changsha 410083,China;School of Geosciences and Info-Physics,Central South University,Changsha 410083,China;MLR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,CAGS,Beijing 100037;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Ministry of Education),Changsha 410083,China [2]School of Geosciences and Info-Physics,Central South University,Changsha 410083,China [3]MLR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,CAGS,Beijing 100037 [4]School of Earth and Space Sciences,Peking University,Beijing 100871,China

出　　处：《Journal of Central South University》2019年第12期3534-3550,共17页中南大学学报（英文版）

基　　金：Projects(41172076,41802080)supported by the National Natural Science Foundation of China;Project(1212011085528)supported by Geological Survey Program from the China Geological Survey;Project(2019CX035)supported by Innovation-driven Plan of Central South University,China;Project(201411025)supported by the Scientific Research Fund from Ministry of Land and Re-sources,China;Project(201309)supported by the Program of High-level Geological Talents,China;Project(201112)supported by the Youth Geological Talents of the China Geological Survey

摘　　要：The ilvaite-bearing skarn associations in the Galinge skarn deposit were studied to determine their physicochemical formation conditions.A thermodynamic model setting pressure of 50 MPa(Pf=Ps=50 MPa)was set up to trace the skarn evolution.Petrographic evidence for replacement of garnet and magnetite by ilvaite in the early retrograde stage(Stage I)combined with thermodynamic modeling suggests that the alteration may have occurred at 400470°C under moderately high fO withΔlgfO(HM)ranges from 4 to 4.2.The model is based on a maximum 22 pressure of 50 MPa calculated from magmatic amphibole geobarometer.The continuous breakdown of ilvaite with quartz to form ferro-actinolite and magnetite occur in the late retrograde stage(Stage II).The reactions occurred at 400440°C under moderate fO(ΔlgfO(HM):4 to 4.4).In Stage III,the breakdown of ilvaite to form calcite,pyrite 22 and ferroactinolite depends on XCO which can be estimated to be in a range of 0.005 to 0.05,and the reaction would 2 occur at higher temperatures with increasing XCO.Under these conditions,the breakdown occurs at 270350°C and 2 low fO(ΔlgfO(HM):up to 5.2).The thermodynamic model for continuous evolution from Stage I to Stage III 22 completely records the conditions of the retrograde alteration,which is inconsistent with the thermobarometry imprints of fluid inclusions.Therefore,the petrography and phase relations of ilvaite are useful indicators of reaction conditions in various skarn deposit types.尕林格大型矽卡岩铁矿位于祁漫塔格斑岩-矽卡岩成矿带内,发育一套典型的Ca质退化蚀变矽卡岩系列。其中,含黑柱石退化蚀变组合可以很好地反演流体交代热动力学过程。岩石学证据表明在早期退化蚀变阶段(Stage I),黑柱石交代石榴子石和磁铁矿,该反应根据岩浆角闪石地质温压计设定最大压力条件50 MPa,获得热动力学T=400~470°C和ΔlgfO2(HM)=4~4.2;在晚期退化蚀变阶段(Stage II),黑柱石和石英反应生成磁铁矿和铁阳起石,该反应发生在400~440°C和ΔlgfO2(HM)=4~4.4热动力学条件范围内;到了方解石-石英-硫化物阶段(Stage III),黑柱石分解形成方解石、黄铁矿和铁阳起石,该反应发生温度随着XCO2的升高而升高,在XCO2=0.0050.05范围内,分解反应条件为T=270350°C和ΔlgfO2(HM)<5.2。随着黑柱石的连续演化,该热动力学模型完整地记录了退化蚀变反应的发生过程。除此之外,流体体系中Fe和Mg的含量会强烈影响黑柱石在矽卡岩体系中的稳定性。因此,黑柱石的岩石学和相变关系可以很好地指示不同类型矽卡岩矿床的交代反应过程。

关 键 词：Galinge skarn deposit ILVAITE retrograde alteration thermodynamic properties 

分 类 号：P61[天文地球—矿床学]