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石英—碳酸盐金矿产于韧性剪切带内的脆性—韧性过渡带中或其上部。已知有些特大型矿床沿长期活动的大型横推剪切带形成。由于深度增大,岩石的粘度减小,所以这种类型的剪切带呈韧性状向下宽度增大。在麻粒岩相变质深度,有些剪切带宽达40Km。韧性剪切带具良好渗透性,流体沿微裂隙渗透,为其发生广泛的化学反应提供了有利条件。由于剪切作用产生热量,矿物中形变作用诱发的应力梯度、以及粒度变小,促使反应速度提高。由于压力降至相当脆性部位,所以流体流总的方向是往上的。在韧性剪切带楔形断面上,从下地壳内穿过很大距离的流体集中在脆性—韧性过渡带中。这样,如果流体在通过下地壳过程中选择地搬运了某些元素,则这些元素也被集中在这种过渡带内。石英—碳酸盐矿脉最常见的特征之一就是碳酸盐化蚀变,这种蚀变在大型矿床向外可扩宽达数公里,CO_2中~(13)C 的特征与地幔源相一致。向上运移的可能为地幔成因的 CO_2气体对岩石从角闪岩相到麻粒岩相的脱水及伴有大离子亲石元素(LILE)的贫化有重要意义。下地壳成分被 CO_2改造这一确证的事实就来自于大型剪切带。深部 CO_2气流只有在比保持石墨稳定更氧化的条件下才能存在。这些条件通过下列几种方式更利于金的溶解,即:(a)Au~0氧化成 Au~+;(b)溶解岩石中的硫化物,并与 Au~+形成络合物。最近研究表明,某些太古代大型金矿就是由较氧化的流体所形成。本文的概念模式至少可以概括一部分石英—碳酸盐金矿床的成因。渗透到深部韧性剪切带中的 CO_2使角闪岩相岩石发生脱水,产生了较氧化的 CO_2—H_2O流体。这种流体在下地壳较大范围内溶解其中的硫化物和金,在较窄的剪切带中金被向上搬运,集中并沉淀在脆性—韧性过渡带中或在其上部。
Quartz-carbonate gold occurs in or above the brittle-ductile transition zone within the ductile shear zone. It is known that some very large deposits are formed along large long-term shear zones. As the depth increases, the viscosity of the rock decreases, so this type of shear band increases in toughness downwards. In the granulite facies metamorphism, some shear bandwidth up to 40Km. The ductile shear zone has a good permeability, and the infiltration of fluids along the micro-cracks provides a favorable condition for a wide range of chemical reactions. Due to the heat generated by the shearing action, the stress gradient induced by the deformation in the mineral, and the smaller particle size, promote the reaction speed. As pressure drops to a fairly brittle location, the general direction of fluid flow is upwards. On the ductile shear zone, the wedge-shaped cross-section of fluid from a large distance through the lower crust is concentrated in the brittle-ductile transition zone. In this way, these elements are also concentrated in this transition zone if the fluid selectively carries certain elements during their passage through the lower crust. One of the most common features of quartz-carbonate veins is carbonate alteration, which can be extended outward by several kilometers in large deposits. The characteristics of ~ (13) C in CO_2 coincide with mantle sources . The upward migration of mantle-derived CO 2 gas may be of great importance for the dehydration of rocks from the amphibolite facies to the granulite facies and the depletion of large LILEs. The corollary of the lower crustal composition being altered by CO2 is the large shear band. Deep CO 2 gas flow is only present more stable than the more stable graphite. These conditions are more conducive to the dissolution of gold by the following ways: (a) Au ~ 0 is oxidized to Au ~ +; (b) the sulfide in the rock is dissolved and forms a complex with Au ~ +. Recent research shows that some of the Archean large-scale gold mines are formed by the more oxidized fluids. The conceptual model in this article at least summarizes the genesis of a portion of the quartz-carbonate gold deposit. CO 2 infiltrated into the deep ductile shear zone dehydrated the amphibolite facies rocks and produced a relatively oxidized CO 2 -H 2 O fluid. This fluid dissolves sulfide and gold within a wide range of the lower crust, and gold is transported upward in the narrower shear zone, concentrating and precipitating in or on the brittle-ductile transition zone.