Stratabound gold deposits in Archean banded iron-formation, Rhodesia
Stratabound gold deposits in Archean banded iron-formation, Rhodesia
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罗得西亚太古代带状铁矿层中的地层金矿床
DOI：
10.2113/gsecongeo.71.1.58
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发表时间：
1976
期刊：
影响因子：
5.8
通讯作者：
R. Fripp
中科院分区：
文献类型：
--
作者：
R. Fripp
层控矿床，特别是金和伴生硫化物，广泛分布在罗得西亚太古代绿岩带的带状铁矿床内。 Vubachikwe 金矿的金矿产状与来自其他八个矿床的矿化铁矿样品一起进行了研究。这些矿场包括 Beehive、Camperdown、Connemara、Empress、Marvel、Nelly 404、Pickstone 和 Sherwood Starr 矿场。在 Vubachikwe 矿场，矿体产于几个带状铁矿层薄层中，这些矿层与镁铁质和长英质水成凝灰岩夹层。这些岩石构成了 Sebakwian 群特有的镁铁质-超镁铁质火山组合的一部分，并被布拉瓦扬群特有的玄武岩和安山岩熔岩和凝灰岩所覆盖。矿体呈层状，局限于硫化物床和混合硫化物-碳酸盐相带状铁矿层，由交替富含石英（燧石）、毒砂、磁黄铁矿和铁白云石的层组成。金被包裹在毒砂颗粒内，平均矿石品位为 11 ppm。岩相学和构造证据表明金和硫化物在年龄上是前变质和预变形的。有人提出，对于所有研究的矿床，金、硫化物和铁地层是密切相关的。关于金溶解度的实验证据和来自活跃富马罗阶段地热区的数据支持这样的观点，即热盐水能够将大量金和其他金属作为可溶性络离子输送到地表。带状铁矿、硫化物和金的起源的火山成因模型受到青睐。此类矿床被认为代表了从水下（也可能是陆上）活跃喷气孔挤出的溶液沉积的海底化学沉淀物。这些层控矿床的分布受到区域地层控制，其中大部分发生在与下部镁铁质-超镁铁质火山组合（Sebakwian 群）相关的铁矿层中。
Stratabound mineral deposits, particularly of gold and associated sulfides, are widely distributed within beds of banded iron-formation in the Archean greenstone belts of Rhodesia. The occurrence of gold at the Vubachikwe gold mine has been studied together with samples of mineralized iron-formation from eight other deposits. These are the Beehive, Camperdown, Connemara, Empress, Marvel, Nelly 404, Pickstone, and Sherwood Starr mines.At the Vubachikwe mine the orebodies occur in several thin beds of banded iron-formation which are interlayered with mafic and felsic aquagene tuffs. These rocks form part of a mafic-ultramafic volcanic assemblage characteristic of the Sebakwian Group and are overlain by basaltic and andesitic lavas and tuffs characteristic of the Bulawayan Group. The orebodies are stratiform and are confined to beds of sulfide and mixed sulfide-carbonate facies banded iron-formation, which consist of layers alternately rich in quartz (cherty), arsenopyrite, pyrrhotite, and ankerite. The gold is occluded within arsenopyrite grains and the average ore grade is 11 ppm. The petrographic and structural evidence indicates that the gold and sulfides are premetamorphic and predeformation in age.It is proposed that, for all the deposits studied, the gold, the sulfides, and the iron-formation are consanguineous. Experimental evidence on gold solubility and data from active fumarolic-stage geothermal areas support the view that thermal brines are capable of transporting significant quantities of gold and other metals to the surface as soluble complex ions. A volcanogenic model for the origin of banded iron-formation, the sulfides, and the gold is favored. Such deposits are considered to represent submarine chemical precipitates deposited from solutions extruded from subaqueous (and possibly subaerial) active fumaroles.There is a regional stratigraphic control to the distribution of these Stratabound mineral deposits, most of which occur in iron-formation associated with the lower mafic-ultramafic volcanic assemblage (Sebakwian Group).