Mineralogy and petrology of iron skarns in western British Columbia, Canada
Mineralogy and petrology of iron skarns in western British Columbia, Canada
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DOI：
10.2113/gsecongeo.79.5.869
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发表时间：
1984-08
期刊：
影响因子：
5.8
通讯作者：
L. Meinert
中科院分区：
文献类型：
--
作者：
L. Meinert
产于不连续带中的钙铁夕卡岩，从加利福尼亚州北部延伸到不列颠哥伦比亚省西部，进入阿拉斯加半岛，形成于大洋岛弧环境，后来增生到大陆地体。这些矽卡岩铁矿床因其规模大、金、钴、铜和锌的稀有元素组合、火成岩原岩以及与“原始”侵入岩和同源火山岩的共同伴生而特别令人感兴趣。一项对不列颠哥伦比亚省西部六个钙铁夕卡岩矿床的对比研究证明，它与其他主要的夕卡岩类型有几个重要的区别。与其他类型的夕卡岩相比，与钙铁夕卡岩伴生的深成岩具有相似的广泛的二氧化硅含量范围，但总体上更具镁铁质；它们的总碱含量相似，但Na2O/K2O比(avg=2.6)高得多。侵入体铁含量与伴生夕卡岩中钙硅酸盐矿物的含铁量成反比，表明夕卡岩中铁的岩浆成分。流体包裹体分析表明，早期相对贫铁的钙硅酸盐矿物形成于较热、相对稀薄的流体(Th=450℃-460℃，3.3wt%氯化钠)，而后来，与磁铁矿共生的富铁硅酸钙矿物形成于较冷的、更多的盐水流体(Th=370℃-460℃，10-50wt%NaCl10-50wt%氯化钠，与局部KCl)。流体包裹体盐度与矽卡岩组分的相关性与实验结果一致，表明溶液中Fe/Al的摩尔比应随氯化物浓度的平方而增大。
Calcic iron skarns present in a discontinuous belt, extending from Northern California through western British Columbia and into the Alaskan peninsula, were formed in an oceanic island-arc environment and later accreted to continental terrane. These iron skarn deposits are of particular interest because of their large size; minor element suite of Au, Co, Cu, and Zn; igneous protoliths; and common association with "primitive" intrusions and cogenetic volcanic rocks. A comparative study of six calcic iron skarn deposits in western British Columbia documents several important differences from other major skarn types. Compared to other skarn types, plutons associated with calcic iron skarns have a similar wide range of silica contents but are generally more mafic, and they have similar total alkali contents but much higher Na 2 O/K 2 O ratios (avg = 2.6). The iron content of intrusions is inversely proportional to the iron content of calc-silicate minerals in associated skarn, suggesting a magmatic component of iron in skarn. Fluid inclusion analyses suggest that early, relatively iron-poor calc-silicate minerals formed from hot, relatively dilute fluids (T h = 450 degrees -460 degrees C, 3.3 wt % NaCl), whereas later, iron-rich calc-silicate minerals associated with magnetite formed from cooler, more saline fluids (T h = 370 degrees -460 degrees C, 10-50 wt % NaCl, with local KCl). The correlation between fluid inclusion salinity and skarn composition is consistent with experimental evidence suggesting that the molar ratio of Fe/Al in solution should increase with the cube of the chloride concentration.--Modified journal abstract.