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DOI:
矿床地质:2009,Vol.>>Issue(5):515-538

初论碰撞造山环境斑岩铜矿成矿模型
中国地质科学院地质研究所
Porphyry Cu deposits in collisional orogen setting: A preliminary genetic model
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中文摘要:作为金属Cu最主要来源的斑岩铜矿床主要产于岛弧及陆缘弧环境。基于大量弧环境斑岩铜矿床研究而建立的经典斑岩铜矿成矿模型,在后来环太平洋成矿带斑岩型矿床的勘查中取得了重大突破,成为科学理论指导矿床勘查的典范。然而,近年来国内矿床学家发现,除经典成矿模型所记录的岛弧及陆缘弧环境外,斑岩铜矿还可产于碰撞造山带内,甚至产在陆内环境中。显然,这些斑岩铜矿的成因无法用经典的斑岩铜矿成矿模型解释。文章从弧环境斑岩铜矿成矿模型的综述入手,通过对青藏高原斑岩铜矿床的成矿环境及构造控制、含矿斑岩起源、矿床基本特征、成矿物质来源、金属富集机制以及成矿流体来源及演化等已有研究成果的综合分析,初步提出了碰撞造山环境斑岩铜矿的成矿模型。该模型强调:① 碰撞造山环境斑岩铜矿含矿斑岩为强烈挤压构造背景下形成的埃达克岩,岩浆起源于加厚的新生下地壳,板块断离或岩石圈拆沉诱发的软流圈物质上涌,以及斜向碰撞导致的挤压-伸展的构造机制转换通常是引发岩浆源区发生部分熔融的外部条件;② 成矿金属的深部富集是因岩浆高氧逸度所致,高氧逸度条件下,S主要以硫酸盐的形式溶解于岩浆之中,从而导致通常优先向硫化物分配的Cu、Au等开始作为不相容元素向硅酸盐熔浆中富集;③ 含矿斑岩的侵位既可受到因斜向碰撞诱发的大型走滑断裂系统的控制,也可受到岩石圈拆沉诱发的大型张性断层的控制;而含矿斑岩的就位则受矿区尺度的构造控制,多组构造的交汇部位或大型背斜的核部常是斑岩铜矿产出的重要位置;④ 大型矿床,特别是超大型矿床下部通常存在岩浆房,岩浆房的流体出溶是引发矿床大规模蚀变与矿化的根源;成矿金属与S均来自岩浆,与含矿斑岩可能具有相同的源区;⑤ 矿床整体上具有与弧环境类似的蚀变分带规律,从内向外依次为钾硅酸盐化、石英_绢云母、粘土化及青磐岩化;不过,因碰撞造山带环境含矿斑岩相对富K,从而导致岩浆房或浅侵的岩株/岩枝中出溶的岩浆热液常具有比弧环境斑岩铜矿床更高的K+/H+比值,从而诱发钾硅酸盐化蚀变的强烈发育;因钾硅酸盐化蚀变持续时间较长,铜钼矿化主要产于该蚀变阶段,特别是以黑云母大量发育为特征的晚期钾硅酸盐化阶段;⑥ 成矿物质沉淀可能因成矿过程中温度、压力、盐度、氧逸度、pH值等因素的变化所致,而这些因素的变化又直接或间接与高原的快速隆升与剥蚀有关。
Abstract:Porphyry Cu deposits (PCDs), as the primary source of copper, are usually thought to be formed in a magmatic arc setting. They can also occur in collisional orogen or intraplate settings. The classic PCDs model, proposed by Lowell and Guilbert (1970), has been widely accepted by economic geologists because of its practical value in the exploration of PCDs in the arc setting, especially in the Circum-Pacific Belt. However, Lowell and Guilbert's model fails to give a reasonable explanation of the PCDs in the collisional orogen setting. The authors therefore give a detailed description of geological setting, tectonic control, magma source, general characteristics of the ore deposit, source and enrichment mechanism of metals, fluid source and evolutionary path of PCDs in the Qinghai-Tibetan collisional orogen setting, and propose a preliminary genetic model. Several points are emphasized in this model: ① Mineralization-related porphyry intrusions in the collisional orogen setting are geochemically adakitic rocks, which originaue from the newly-formed lower crust and are triggered by the upwelling of asthenosphere and/or the transition of structure mechanism from extrusion to extension. ② The enrichment of Cu and other metals in the adakitic magmas results from the relatively high oxidation state of the source, in which the bulk of the sulfur is dissolved in the sulfate form, with the result that sulfide-compatible elements such as Cu and Au can also behave as incompatible elements and will be retained in the evolving magmas.③ The ascent of the adakitic magmas is usually constrained by large-sized strike-slip fault systems triggered by oblique collisionor by large-sized normal faults induced by lithosphere removal, whereas the emplacement of the adakitc magmas is generally controlled by mine-scale structures.④ The magma chamber usually exists below large-sized and, especially, giant deposits. In these deposits, Cu, S and magmatic fluids, which are essential for the formation of porphyry Cu deposits, generally originate directly from the magma chamber. ⑤ The deposits reinforce most of the generalized characteristics of porphyry Cu deposits in continental arc settings, except for the fact that they show relatively strong K-silicate alteration due to high K+/H+ value in the high-K adakitic magma dominated ore-forming fluid. ⑥ Sulfide precipitation mainly occurs during K-silicate alteration, usually in response to the change of temperature, pressure, salinity, f(O2), and pH value, especially to the change of temperature and pressure.
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基金项目:国家基础研究规划973项目(2009CB421004-1)和国家自然科学重点基金(40730419)
引用文本:
杨志明,侯增谦.2009.初论碰撞造山环境斑岩铜矿成矿模型[J].矿床地质,28(5):515~538
.2009.Porphyry Cu deposits in collisional orogen setting: A preliminary genetic model[J].Mineral Deposits28(5):515~538
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