Rare earth elements, protoliths, and alteration at the Hemlo gold deposit, Ontario, Canada, and comparison with argillic and sericitic alteration in the Highland Valley porphyry district, British Columbia, Canada
Rare earth elements, protoliths, and alteration at the Hemlo gold deposit, Ontario, Canada, and comparison with argillic and sericitic alteration in the Highland Valley porphyry district, British Columbia, Canada
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加拿大安大略省 Hemlo 金矿的稀土元素、原岩和蚀变，以及与加拿大不列颠哥伦比亚省 Highland Valley 斑岩区的泥质和绢云母蚀变的比较
DOI：
10.2113/gsecongeo.92.5.551
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发表时间：
1997
期刊：
影响因子：
5.8
通讯作者：
M. Seller
中科院分区：
文献类型：
--
作者：
M. Fleet;M. Seller
稀土元素（REE）、Sc和Th被用于确定安大略Hemlo金存款中两种重要的蚀变和矿化原岩：石英-长石斑岩和绿岩（变质沉积岩和变质火山岩），主要为中基性成分。存款的稀土元素地球化学基本上是被动的普遍和特征的微斜长石蚀变。而以Al 2 O3为不动组分时，稀土元素，特别是轻稀土元素、TiO 2和Zr在其他蚀变类型中具有活动性。稀释稀土元素丰度的次生矿物（黄铁矿，重晶石，石英，碳酸盐）平均X 2.0，轻稀土浸出损失平均为56%的斑岩原岩，X 1.6和68%，分别在矿石中的绿岩原岩。而大多数的次生矿物稀释稀土元素丰度结晶广泛同期微斜长石，轻稀土元素的浸出最有可能发生在晚钙硅酸盐蚀变事件。轻稀土元素的亏损，如减少（La/Yb）N，增加与Au含量的金矿石来源于斑岩和绿岩原岩。然而，稀土元素地球化学仍以原岩成分为主，因此，不是一个合适的主要工具，寻找Hemlo型金矿。不列颠哥伦比亚省高地谷斑岩区的泥质蚀变与全岩蚀变和绢云母蚀变相比，稀土元素均匀富集（<或= X2）。在Al 2 O3-（CaO + Na 2 O）-K2 O三元相图中，泥质和绢云母蚀变分离物定义了一个特征性的线性趋势，这与Hemlo存款上盘的铝质岩石的成分场不同。后者岩石的地球化学和区域产状清楚地表明它们是变岩。
Rare earth elements (REE), Sc, and Th are used to identify two volume-important protoliths for alteration and mineralization at the Hemlo gold deposit, Ontario: quartz-feldspar porphyry and greenstone (metasedimentary and metavolcanic rocks) of predominant intermediate-mafic composition. The REE geochemistry was essentially passive to the pervasive and characteristic microcline alteration at the deposit. However, using Al 2 O 3 as the immobile component, there is evidence for mobility of REE, particularly of light REE, TiO 2 , and Zr in other styles of alteration. Dilution of REE abundances by secondary minerals (pyrite, barite, quartz, and carbonates) averaged X 2.0, and loss of light REE to leaching averaged 56 percent in ores of the porphyry protolith, and X 1.6 and 68 percent, respectively, in ores of the greenstone protolith. Whereas most of the secondary minerals diluting REE abundances crystallized broadly contemporaneously with microcline, leaching of light REE most likely occurred later during the late calc-silicate alteration event. Depletion of light REE, as measured by a decrease in (La/Yb) N , increases with an increase in Au content for gold ores derived from both porphyry and greenstone protoliths. However, the REE geochemistry remains dominated by the protolith composition and, thus, is not a suitable primary tool for exploration for Hemlo-type gold deposits. Argillic alteration in the Highland Valley porphyry district, British Columbia, is uniformly enriched in REE (< or = X 2) compared with incipiently to intensely altered whole rocks and sericitic alteration. The argillic and sericitic alteration separates define a characteristic linear trend in the Al 2 O 3 -(CaO + Na 2 O)-K 2 O ternary diagram that is distinct from the composition field for aluminous rocks of the hanging wall of the Hemlo deposit. The geochemistry and regional occurrence of these latter rocks clearly indicate that they are metapelites.