A hydrogen and oxygen isotope study of the San Cristobal Mine, Peru; implications of the role of water to rock ratio for the genesis of wolframite deposits
A hydrogen and oxygen isotope study of the San Cristobal Mine, Peru; implications of the role of water to rock ratio for the genesis of wolframite deposits
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DOI：
10.2113/gsecongeo.79.8.1818
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发表时间：
1984-12
期刊：
影响因子：
5.8
通讯作者：
A. Campbell;D. Rye;U. Petersen
中科院分区：
文献类型：
--
作者：
A. Campbell;D. Rye;U. Petersen
测定了秘鲁圣克里斯托瓦尔黑钨贱金属矿床脉状矿物和提取的流体包裹体水的氧、氢同位素比值。石英的氧同位素值为9.8~14.4‰，黑钨矿的氧同位素为0.6‰~4.6‰。在300摄氏度时，水与石英和黑钨矿平衡时的Delta值计算为：Delta18O=2.8-7.3/mil(石英)和1.4-5.4/mil(黑钨矿)。氢同位素值显示的总体范围是D=-58到-148/mil，但任何给定矿物的范围都要小得多。这些数据是根据一个模型解释的，该模型考察了温度和水岩比对与花岗岩交换的大气降水的同位素组成的影响。在以岩石为主的体系中，随着交换温度的降低，同位素交换水在18O三角洲变得贫化，而在D三角洲变富。当水与岩石的比例也允许变化时，会产生各种各样的水成分。圣克里斯托瓦尔矿物的同位素组成可以解释为大气降水在400摄氏度与花岗岩进行了同位素交换的结果，水与岩石的比率在0.01%到0.003之间。从另外两个黑钨矿床Pasto Bueno(Landis，1972)和Panasquiera(Kelly and Rye，1979)获得的同位素数据用为San Cristobal开发的模型进行了重新解释。这两组数据都符合这样的假设，即黑钨矿矿床是由经历了极低水岩比(<；0.05)交换的大气水形成的。低水岩比的重要性可能与钨从结晶岩体中浸出的方式有关。
Oxygen and hydrogen isotope ratios were measured from vein minerals and extracted fluid inclusion waters from the San Cristobal wolframite-base metal deposit in Peru. Oxygen isotope values for quartz range from 9.8 to 14.4 per mil and for wolframite from 0.6 to 4.6 per mil. The calculated delta values at 300 degrees C for water in equilibrium with quartz and wolframite are delta 18 O = 2.8 to 7.3 per mil for quartz and 1.4 to 5.4 per mil for wolframite. Hydrogen isotope values show an overall range of delta D = -58 to -148 per mil, but the range for any given mineral is much smaller. These data are interpreted in light of a model which examines the effect of temperature and water to rock ratio on the isotopic compositions of meteoric waters exchanging with granite. In a rock-dominated system an isotopically exchanged water becomes depleted in delta 18 O and enriched in delta D as the temperature of exchange decreases. When the water to rock ratio is also allowed to vary, a wide variety of water compositions is generated. The isotopic composition of minerals from San Cristobal can be interpreted as the result of deposition from a meteoric water which has undergone isotopic exchange with a granite at 400 degrees C, with a water to rock ratio ranging from 0.01 to 0.003. Isotopic data taken from two other wolframite deposits, Pasto Bueno (Landis, 1972) and Panasquiera (Kelly and Rye, 1979) are reinterpreted using the model developed for San Cristobal. Both sets of data are consistent with the hypothesis that wolframite deposits are formed by meteoric waters which have experienced exchange at very low water to rock ratios (<0.05). The importance of the low water to rock ratio may be related to the way in which tungsten is leached from a crystallized pluton.