含碳质地层对矽卡岩钨矿的影响——以鄂东付家山钨矿床为例

付家山矽卡岩钨矿床位于长江中下游成矿带鄂东矿集区,矿体产于晚中生代花岗闪长斑岩体与下二叠统含碳质地层的接触带。付家山矿区西侧地层为茅口组灰岩,东侧地层为栖霞组灰岩,茅口组灰岩中有机碳含量(0.72%)低于栖霞组灰岩(0.95%)。为了探明不同地层对矽卡岩钨矿床的矿物成分的影响,文章针对付家山矽卡岩钨矿的地层、矽卡岩矿物和白钨矿进行详细地野外地质观察和编录,并利用电子探针(EMPA)开展矿物成分分析。东、西侧地层中矽卡岩阶段的石榴子石和辉石有明显差异,与茅口组接触交代形成的石榴子石变化范围较小(And_(31～90)Gro_(1～53)Spr_(5～20)),辉石端员成分变化范围变化较大(Di_(0～100)Hd_(0～97));而与栖霞组接触交代形成的石榴子石变化范围较大,主要为And_(66～95)Gro_(0～27)Spr_(3～7),部分为And_(19～33)Gro_(60～76)Spr_(3～7)。辉石端员成分为Di_(44～64)Hd_(29～49(。西侧矿段石英-硫化物阶段和方解石阶段中白钨矿的MoO_3相较于东侧矿段含量要高,产于茅口组矿体的石英-硫化物和方解石阶段白钨矿w(MoO_3)为0～1.82%,产于栖霞组矿体的石英-硫化物和方解石阶段白钨矿w(MoO_3)为0.08%～0.86%。上述矿物组合暗示付家山西侧矿段相较于东侧矿段形成环境更为氧化,表明含碳量不同的地层对矽卡岩钨矿的形成有明显的影响。

Influence of carbonaceous strata on skarn tungsten deposits: A case study of Fujiashan deposit in eastern Hubei Province

The Fujiashan skarn tungsten deposit is located in the Edong ore cluster of the Middle-Lower Yangtze Valley metallogenic belt (MLYRB). Tungsten orebodies are mainly developed along the contact zone between late Mesozoic granite diorite porphyry and the lower Permian strata. The western wall rock of Fujiashan segment is Permian Maokou Formation carbonate rocks, while the eastern segment is Permian Chihsia Formation carbo-nate rocks. The total organic carbon content of the Maokou Formation (0.72%) is lower than the Chihsia Formation (0.95%). To ascertain the influence of different strata on minerals of skarn tungsten deposit, the authors conducted detailed field observation and electron microprobe analysis (EPMA) of skarn minerals and scheelite. There are obvious differences between composition of garnet and that of pyroxenes in the western segment and the eastern segment. The garnets hosted in the Maokou Formation are And_31~90Gro_1~53Spr_5~20, and pyroxenes has a wide range (Di_0~100Hd_0~97). The garnets hosted in the Chihsia Formation are And_66~95Gro_0~27Spr_3~7, with a part being And_19~33Gro_60~76Spr_3~7, and pyroxenes is Di_44~64Hd_29~49. The MoO₃ values of scheelite at both quartz-sulfide stage and calcite stage in the western segment are higher than the values in the eastern segment. The scheelite hosted in the Maokou Formation of the quartz-sulfide and calcite stage shows high concentration of MoO₃ (0~1.82%), while scheelite hosted in the Chihsia Formation at the quartz-sulfide stage and calcite stage have low concentration of MoO 3 (0.08%~0.86%). The above features suggest that the mineral composition in the western segment is more oxidized than that in the eastern segment, which indicates that the strata with different organic values had obvious influence on the formation of skarn tungsten deposit.