Abstract

For the first time, from the standpoint of magmatism and subsequent hydrothermal–metasomatic alteration, sulfide and platinum-metal mineral assemblages of rocks of ore-bearing intrusions of the Khudolaz Complex have been characterized. Four types of assemblages have been identified: (1) pentlandite–chalcopyrite–pyrrhotite in the form of drop-shaped and interstitial disseminations with inclusions of sperrylite, moncheite, michenerite, merenskyite, froodite; (2) complex amoebalike inclusions with the composition pyrite ± pyrrhotite–chalcopyrite–violarite ± pentlandite with inclusions of Sb–michenerite, sudburyite, and borovskite; (3) newly formed pyrite–chalcopyrite veins and patches in intensely metasomatized rocks; (4) additionally-formed euhedral pyrite disseminations in metasomatites along zones intersected by dolerite dikes. The formation of these sulfide–platinum-metal assemblages occurred in three stages: (1) magmatic and late magmatic (type 1), 2) hydrothermal–early medium temperature and late low-temperature (types 2, 3), (3) repeated hydrothermal–low–medium temperature (type 4). It is shown that the crystallization of sulfide minerals occurred in a wide temperature range (about 1000–200°C). PGE minerals separated at the late magmatic stage during cooling of a highly fractionated sulfide or immiscible chalcogenide melt and during decomposition of sulfide solid solutions (T ~ 650–300°C). At the early hydrothermal stage (T ~ 300–250°C), pyrrhotite was replaced by pyrite; pentlandite, by violarite; a significant amount of Ni and Co from primary sulfides was inherited by secondary sulfides. Primary chalcopyrite was mainly replaced by silicates (chlorite, amphibole, etc.). It is suggested that the antimony minerals of Pd (including high-antimony michenerite with Sb up to 0.46 apfu) could have crystallized from an Sb-enriched hydrothermal fluid. Host rocks could have been an additional source of antimony in the fluid. At the late hydrothermal stage (T < 200°C), significant dissolution of primary sulfide and platinum-metal phases occurred with redeposition in the upper parts of massifs and in host rocks. The recurring hydrothermal process (T ≤ 200°C) was associated with emplacement of dikes of the Ulugurtau complex and new redeposition of sulfides along zones of fluid action.

中文翻译：

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Khudolaz 杂岩体（南乌拉尔）的多阶段岩浆-热液硫化物-PGE 矿化

摘要

从岩浆作用和随后的热液-交代蚀变的角度，首次表征了 Khudolaz 杂岩体含矿侵入岩的硫化物和铂金属矿物组合。已经确定了四种类型的组合：（1）呈滴状和间隙散布形式的镍黄铁矿-黄铜矿-磁黄铁矿，其中包含有闪锌矿、蒙脱石、镁锌矿、美伦斯基矿、弗洛迪特；(2) 复杂的变形虫类包裹体，其组成为黄铁矿±磁黄铁矿-黄铜矿-紫铜矿±镍黄铁矿，其中含有 Sb-michenerite、sudburyite 和 borovskite 包裹体；(3)强烈交代岩石中新形成的黄铁矿-黄铜矿脉和斑块；(4) 加成自形黄铁矿在交代岩中沿着与辉绿岩脉相交的区域分布。这些硫化物-铂-金属组合的形成经历了三个阶段：（1）岩浆和晚期岩浆（1型），2）热液-早中温和晚期低温（2、3型），（3）重复热液-中低温（类型4）。结果表明，硫化矿物的结晶发生在很宽的温度范围内（约 1000-200°C）。PGE 矿物在岩浆后期在高度分馏的硫化物或不混溶的硫属化物熔体冷却和硫化物固溶体分解期间分离（T ~ 650-300°C）。在早期热液阶段（T~ 300–250°C)，磁黄铁矿被黄铁矿取代；pentlandite，由紫罗兰；来自一次硫化物的大量 Ni 和 Co 被二次硫化物继承。原生黄铜矿主要被硅酸盐（绿泥石、角闪石等）取代。这表明 Pd 的锑矿物（包括含高达 0.46 apfu 的 Sb 的高锑云柱石）可能是从富含 Sb 的热液流体中结晶出来的。母岩可能是流体中锑的另一个来源。在热液后期（T < 200°C），原生硫化物和铂金属相发生显着溶解，并在地块上部和主岩中重新沉积。反复发生的热液过程（T ≤ 200°C) 与 Ulugurtau 复合岩脉的就位和沿流体作用区的硫化物的新再沉积有关。