引用本文：王新雨,祝新友,李加多,王玉往,龙灵利,李顺庭,吴锦荣,程细音,蒋斌斌.2020.青海牛苦头矿区锰质黑柱石成因及其地质意义[J].地质学报,94(8):2279-2290. WANG Xinyu,ZHU Xinyou,LI Jiaduo,WANG Yuwang,LONG Lingli,LI Shunting,WU Jinrong,CHENG Xiyin,JIANG Binbin.2020.Genesis and geological significance of manganilvaite in the Niukutou deposit, Qinghai Province[J].Acta Geologica Sinica,94(8):2279-2290.
Abstract:Ilvaite, a common calcium silicate mineral in skarn- type deposit, which is associated with the Pb- Zn mineralization closely. In this study, the optical property, mineral association and chemical composition of ilvaite in Niukutou deposit are discussed. There are three ilvaite- bearing association in the Niukutou deposit: (1) Ilvaite+garnet+magnetite mineral assemblage; (2) Ilvaite+mangan- hedenbergite (Mn- Hd)+johannsenite (Jo)+galena+magnetite mineral assemblage; (3) Ilvaite+calcite+quartz+sulfide (pyrite, pyrrhotite and other sulfide) mineral assemblage, and formed a garnet- magnetite+ilvaite+
johannsenite skarn zonation outward from the skarn- related pluton. These three mineral associations are corresponding to three mineralization phases, respectively. Stage Ⅰ, the prograde garnet was replaced by the ilvaite. Stage Ⅱ, the mangan- hedenbergite (Mn- Hd) or johannsenite (Jo) were replaced by the manganilvaite. Stage Ⅲ，similar to quartz sulfide stage, the further breakdown of ilvaite produced magnetite, calcite and quartz. The mineral chemical composition by EPMA showed that the molecular formula of the Niukutou ilvaiteis Ca 0. 94- 0. 98 (Fe 1. 22- 1. 92 Mn 0. 10- 0. 75 Mg 0. 01- 0. 03 ) 2+ (2. 00- 2. 05) (Fe 0. 83- 0. 93 Al 0. 01- 0. 07) 3+ (0. 82- 1. 03) \[Si 2. 00- 2. 07 O7\]O(OH). The in situ LA- ICP- MS trace element analysis showed that the REE patterns of ilvaites are similar to the prograde garnet- pyroxene, which is an evidence for their inheritance in the hydrothermal process. Together with the mineral assemblage, we suggest that ilvaite originated from the continuous alteration and replacement of the early skarn silicates. The skarn zonation in Niukutou deposit is indicative of evolution of the hydrothermal process from reducing (Fe 2+ , Mn 2+ ) during the formation of the primary skarns, to hydrated and more oxidizing (with Fe 2+ , Mn 2+ +Fe 3+ , and then Fe 3+ ) during the overlapping retrograde alterations and deposition of the ore minerals.