Oxygen and Carbon Isotope Studies on the Skarn-Type Ores at the Tengumori Copper Deposit of the Kamaishi Mine, Northeastern Japan
Oxygen and Carbon Isotope Studies on the Skarn-Type Ores at the Tengumori Copper Deposit of the Kamaishi Mine, Northeastern Japan
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日本东北部釜石矿天守铜矿床矽卡岩型矿石的氧和碳同位素研究
DOI：
10.11456/shigenchishitsu1992.46.125
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
H. Ohmoto
中科院分区：
文献类型：
--
作者：
M. Haruna;H. Ohmoto
日本东北部釜石矿的天古森矿床是发育在白垩纪花岗质侵入岩附近的矽卡岩型铜矿床。Tengumori矿床的热液活动可分为3个阶段：1)钙硅酸盐（可分为斜辉石期和石榴石期），2)矿石成矿（黄铜矿+磁黄铁矿+石英），3)方解石。确定ƒÂ18O （SMOW）值为：斜辉石（钙硅酸盐阶段，7个样品）+6.6 ~ +7.8•ñ，石榴石（钙硅酸盐阶段，14个样品）+4.2 ~ +7.0•ñ，石英（矿化阶段，13个样品）+12.0 ~ +13.7•ñ，方解石（方解石阶段，19个样品）+10.6 ~ +12.8•ñ。从共存（但不是同时期）矿物对计算的氧同位素温度给出了一致的值•330-460•Ž。但均高于流体包裹体的压力校正均一温度（•180 ~ 330•Ž）和黄铜矿和六方磁黄铁矿的最高稳定温度（325•Ž）。这种温度差异是由于在钙硅酸盐阶段ƒÂ18OH2O值由•′+7变为+9•ñ，在矿化阶段由•′+2变为+7•ñ，在方解石阶段由+1变为+5•ñ。钙硅酸盐阶段溶液的ƒÂ18O值可以解释为未交换的岩浆水或与寄主岩石平衡的水。矿化阶段的热液要么是岩浆水与冷却的岩体部分再平衡的水，要么是与乡村岩石平衡的水，要么是与外来水（如当地大气水）的混合溶液。方解石晶体（方解石阶段）的ƒÂ13C （PDB）值范围为-5.44 ~ -0.37•ñ。计算得到的热液ƒÂ13CH2CO3值在-5.8 ~ +1.4•ñ之间，表明碳来源于花岗质岩浆和寄主灰岩。岩浆流体对方解石级溶液的贡献可以从方解石晶体的高盐度值（高达23 wt. %当量NaCl）和ƒÂ13C值中识别出来。
The Tengumori deposit of the Kamaishi mine, Northeastern Japan, is a skarn-type copper ore deposit that devel ops near granitic intrusive rocks of Cretaceous age. Hydrothermal activity at the Tengumori deposit is divisible into three stages: 1) calc-silicate (divisible into clinopyroxene and garnet phases), 2) ore mineralization (chalcopyrite+pyrrhotite+ quartz), and 3) calcite. The ƒÂ18O (SMOW) values were determined to be: +6.6to +7.8•ñ for clinopyroxene (calc-silicate stage, 7 samples), +4.2 to +7.0•ñ for garnet (calc-silicate stage, 14 samples), +12.0 to +13.7•ñ for quartz (ore mineraliza tion stage, 13 samples), and +10.6 to +12.8•ñ for calcite (calcite stage, 19 samples). The oxygen isotopic temperatures calculated from the coexisting (but not contemporaneous) mineral pairs give consistent values of •`330-460•Ž. However, they are higher than both of the pressure-corrected homogenization temperatures of fluid inclusions (•`180-330•Ž) and the uppermost temperature of stability of chalcopyrite and hexagonal pyrrhotite (325•Ž). This temperature discrepancy is the result of changing ƒÂ18OH2O value from •`+7 to +9•ñ in the cal-silicate stage, •`+2 to +7•ñ in the ore mineralization stage, and +1 to +5•ñ in the calcite stage. The ƒÂ18O values of the calc-silicate stage solution can be interpreted as the unexchanged magmatic water or water in equilibrium with the host rocks. The hydrothermal solution of the ore mineralization stage is either magmatic water partially reequilibrated with the cooling pluton, water in equilibrium with the country rocks, or mixed solution with externally-derived water, e.g., local meteoric water. The ƒÂ13C (PDB) values of calcite crystals (calcite stage) range from -5.44 to -0.37•ñ. The calculated ƒÂ13CH2CO3 values of the hydrothermal solution range from -5.8 to +1.4•ñ and suggest that carbon was derived from both the granitic magma and the host limestone. Contributions of magmatic fluids to the calcite stage solution were recognized from the high salinity values (up to 23 wt. % equivalent NaCl) and the ƒÂ13C values of the calcite crystals.