新疆喀拉通克铜镍硫化物矿床成矿作用与深部地质过程

The Kalatongke mafic intrusions host the largest Cu-Ni sulfide deposits in Xinjiang. The host intrusions are characterized by small sizes and highly evolved parental magma composition. The sulfide ores are characterized by higher Cu/Ni ratios than other major magmatic Ni-Cu deposits in the world. The present study focuses on some outstanding questions such as (1) the nature of parental magma, (2) causes of sulfur saturation (i.e., crustal contamination, mixing with coeval granitic melt, fractional crystallization), (3) controls on the compositional variations of bulk sulfide ores, and (4) the mechanisms of sulfide liquid transportation and accumulation. Our new approaches will include (1) Lu-Hf isotopes of zircons by LA-ICP-MS, (2) REE and HFSE in clinopyroxene by LA-ICP-MS, and (3) H-O isotopes of hornblende separates by TIMS. These new data, together with complimentary data to be acquired such as mineral chemistry (olivine, pyroxenes and hornblende), whole rock major + trace element compositions, the concentrations of PGE-Cu-Ni-Co-Au-S-As-Sb-Bi-Te in sulfide ores, and S isotopes to evaluate the controlling factors in the formation of the Kalatongke-type magmatic Ni-Cu deposits. Special attention will be paid to the processes that took place at depth below final magma emplacement at Kalatongke. The ultimate goal of this study is to construct a more realistic genetic model that can be used to guide regional exploration for the Kalatongke-type Ni-Cu sulfide deposit.

喀拉通克镁铁质侵入体赋存大型铜镍硫化物矿床，含矿岩体小且母岩浆演化程度高，矿石Cu/Ni值高于世界上大多数岩浆Ni-Cu矿床。对该矿床的研究尚存在有待深入探讨的问题：①母岩浆性质；②硫饱和的原因（地壳混染，同期花岗质熔体的混合，分离结晶）；③块状矿石组分变化的控制因素；④硫化物熔体运移和聚积机制。本项目以新的方法开展研究：①锆石Lu-Hf同位素LA-MC-ICPMS分析；②单斜辉石REE和HFSE的LA-ICP-MS分析；③角闪石H-O同位素TIMS分析。运用新数据，结合已有矿物化学组分（橄榄石、辉石、角闪石）、全岩主量和微量元素成分、矿石PGE-Cu-Ni-Co-Au等含量和S同位素等数据，探讨喀拉通克型岩浆铜镍硫化物矿床成矿作用中的控制因素。研究聚焦点是该矿床岩浆最终就位前所发生的深部地质过程，目标是构建更具实际意义的矿床成因模式，服务于喀拉通克型Ni-Cu硫化物矿床的勘查实践。

新疆喀拉通克岩浆铜镍硫化物矿床，矿区已发现镁铁质岩体13个，工业矿体集中在Y1、Y2、Y3和Y9中。本项目对该矿区镁铁质岩体进行了系统的年代学、岩石地球化学和同位素研究。锆石U-Pb定年，Y3岩体苏长岩和闪长岩年龄分别为283.8 ± 1.5Ma和290.4 ± 1.5 Ma，Y9岩体辉长岩为288.3 ± 2.7 Ma，Y5岩体辉长岩和闪长岩分别为320.5 ± 2.5 Ma和320.4 ± 1.1 Ma。结合地球化学研究，认为晚石炭世Y5岩体形成于板块俯冲作用过程中地幔楔底部部分熔融形成的玄武质岩浆，早二叠世Y1等岩体（290 – 281 Ma）形成于俯冲之后，由于上覆岩石圈拆沉导致软流圈减压熔融形成的玄武质岩浆。Sr-Nd-Hf-O-S同位素研究，Y2、Y3和G21岩体中磷灰石的εNd(t)和(87Sr/86Sr)i范围相近，分别为3.55–5.69和0.7045–0.7047；Y2、Y3和G21岩体锆石Hf同位素相似，(176Hf/177Hf)i和εHf(t)分别为0.2829–0.2830和9.4–16.5；Y3岩体苏长岩、闪长岩和G21岩体辉长岩中锆石δ18Ozircon平均值分别为6.54±0.18 ‰、6.25±0.12 ‰和6.45±0.13 ‰。由此估算，含矿岩体的岩浆经历了最高可达15wt.%地壳物质混染。Y1、Y2、Y3、Y9和G21岩体中硫化物δ34S值为-1.9 – -2.8‰、0.4 – -2.5 ‰、-0.9 – -3.1 ‰、-1.5 – -2.5 ‰和-2.0 – -2.2 ‰，显示岩浆在侵位过程中有地壳硫加入。由此论证了该矿床硫饱和的主要控制因素为分离结晶、地壳混染和外源硫的加入。本研究成果丰富了造山带岩浆铜镍硫化物矿床的理论研究，对矿区深部及外围区域找矿具有重要理论及实际意义。