First Occurrence of Ilvaite in a Gold Skarn Deposit
First Occurrence of Ilvaite in a Gold Skarn Deposit
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DOI：
10.2113/gsecongeo.97.5.1119
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发表时间：
2002-08
期刊：
影响因子：
5.8
通讯作者：
M. Franchini;L. Meinert;J. M. Vallés
中科院分区：
文献类型：
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作者：
M. Franchini;L. Meinert;J. M. Vallés
在内华达州的Fortitude Au矽卡岩矿床中发现了伊利瓦石，这是首次报道的在Au矽卡岩存款中发现伊利瓦石。钛铁矿是一种混合价态的钙和铁硅酸盐，以前被认为是一些锌（铅）、铁和锡夕卡岩中相对罕见的矿物。在Fortitude，黑硅钙石以黑色颗粒状存在，含石英、铁阳起石和硫化物（磁黄铁矿-毒砂-辉铋矿）。它也以晚期相的形式出现，取代夕卡岩-大理岩接触面附近富磁铁矿夕卡岩中的辉石岩（Hd 91 - 96 Jo 3 - 5），并取代大理岩前缘的方解石颗粒。电子探针分析表明，来自Fortitude Au-矽卡岩的黑云母在成分上与来自Fe-矽卡岩的黑云母相似。相对于锌夕卡岩，两者都具有高铁和低锰。铁和Au矽卡岩中的黑云母中的高铁含量与表征两种矽卡岩类型及其相关侵入体的高铁活动和低fO 2条件相一致。类似地，来自锌矽卡岩的钛铁矿反映了这些矿床的富锰矿物学。与来自其他夕卡岩类型的黑云母相比，来自一个锡夕卡岩矿点的黑云母具有更高的Al 2 O3和TiO 2以及更低的MnO和Fe +3，并且FeO总量介于来自Zn的黑云母和Fe-Au夕卡岩的黑云母之间。橄榄岩的Al 2 O3和TiO 2含量与伴生侵入体的Al 2 O3和TiO 2含量成反比。虽然在大多数矽卡岩中它是一种罕见的矿物，但这些观察结果表明，可以利用黑硅钙石的产状和成分来区分不同的矽卡岩存款类型，并提供有关形成的地质和地球化学环境的信息。
Ilvaite occurs in the Fortitude Au skarn deposit, Nevada, the first reported occurrence in a Au skarn deposit. Ilvaite is a mixed-valence calcium and iron silicate known previously as a relatively rare mineral in some Zn(Pb), Fe, and Sn skarns. At Fortitude, ilvaite is present as resinous, black grains with quartz, ferroactinolite, and sulfides (pyrrhotite-arsenopyrite-bismuthinite). It also occurs as a late-phase replacing prograde pyroxene (Hd 91 –96 Jo 3 –5 ) in magnetite-rich exoskarn near the skarn-marble contact and replacing calcite grains at the marble front. Electron microprobe analyses show that the ilvaite from the Fortitude Au-skarn is similar in composition to ilvaite from Fe skarns. Both have high iron and low manganese relative to Zn skarns. The high iron content in ilvaite from Fe and Au skarns is consistent with the high-Fe activities and low- f O 2 conditions that characterize both skarn types and their associated intrusions. Similarly, the ilvaite from Zn skarns reflects the Mn-rich mineralogy of these deposits. Ilvaite from one Sn skarn occurrence has higher Al 2 O 3 and TiO 2 and lower MnO and Fe +3 than ilvaite from the other skarn types and FeO totals intermediate between ilvaite from Zn and Fe-Au skarns. The Al 2 O 3 and TiO 2 content of ilvaite appears to be inversely proportional to that of the associated intrusions. Although it is a rare mineral in most skarns, these observations suggest that the occurrence and composition of ilvaite can be used to discriminate among different skarn deposit types and to provide information about the geological and geochemical environment of formation.