中亚萨亚克大型铜矿田矽卡岩型铜成矿作用的年代学制约

萨亚克铜矿田是中亚成矿域巴尔喀什成矿带唯一的以矽卡岩型铜矿化为主的大型铜矿床,产在哈萨克斯坦的萨亚克复向斜内。铜矿田包括了几个在空间上相对独立的矽卡岩型铜矿床、斑岩型铜钼网状脉矿床和一系列石英脉型矿脉,构成了斑岩型和矽卡岩型两个端元形成的成矿系列,但以矽卡岩型为主。铜矿田花岗岩类岩石的锆石SHRIMPU-Pb定年,给出了两期与矽卡岩型铜成矿作用有关的深成岩浆作用的时代,早期的闪长岩结晶年龄为335±2Ma,晚期的花岗闪长岩结晶年龄为308±10Ma,反映了两期矽卡岩型铜成矿作用的年龄。结合成矿元素分析,认为早期335±2Ma为主要成矿期年龄,而308±10Ma为次要成矿期年龄。区域成矿时代的分析表明,主矽卡岩型成矿期先于区域的斑岩型铜成矿作用而发生,次要的矽卡岩型成矿期略晚于区域斑岩铜成矿期。花岗岩类岩石中的角闪石、黑云母、钾长石40Ar/39Ar测年结果进一步限定了矽卡岩型铜成矿作用的时代,分别给出冷却年龄为286.6±6.7Ma、306.6±2.9Ma和257±11Ma。4个花岗岩类岩石中的磷灰石裂变径迹测年和热历史模拟给出年龄范围为85.4±4.5Ma至66.9±4.1Ma,说明了矽卡岩型萨亚克铜矿田的剥露作用主要发生在晚白垩世晚期。本文花岗岩类岩石的U-Pb、40Ar/39Ar和裂变径迹热年代学研究,揭示了萨亚克铜矿田从深成的岩浆侵入活动、成矿作用、区域冷却到剥露作用的全过程。

Geochronological constraints on skarn copper metallogenesis of the large-scale Sayak ore field, Kazakhstan, Central Asia

The Sayak ore field, composed of several separated skarn Cu and porphyry Cu-Mo deposits and Cu-Au-Mo lodes in the Sayak synclinorium, is the only one area with the occurrence of large-scale skarn Cu deposits in the Balkhash metallogenic belt, Kazakhstan, Central Asia. It consists of a metallogenic series with skarn and porphyry deposits as the two end members. Zircon SHRIMP U-Pb geochronology of the skarn-related granitoids presents three phases of pluton intrusions in the Middle to Late Hercynian at 335±2Ma (diorite), 308±10Ma (granodiorite), and 297±3Ma (monzonite), respectively. The first two phases of intrusions are consistent with the skarn Cu metallogenesis, suggesting the main and secondary skarn Cu metallogenic ages at 335±2Ma and 308±10Ma, before and after the regional main porphyry Cu metallogenesis, respectively. ⁴⁰Ar/³⁹Ar thermochronology of hornblede, biotite, and K-feldspar from granitoids gives the cooling ages at 286.6±6.7Ma, 306.6±2.9Ma, and 257±11Ma, respectively, constraining the skarn metallogenic time further more. Apatite fission track dating and thermal history modeling of granitoids gives low temperature cooling ages ranging from 85.4±4.5Ma to 66.9±4.1Ma, suggesting the uplifting and exhumation of the skarn Cu deposits together with the granitoids during the Late Cretaceous in the Sayak ore field. The geochronological data presented in this paper, together with metallogenic information from previous studies, reveal the entire thermo-history, from the intrusion of plutons and skarn metallogenesis in the abyssal system, and regional cooling, to the exhumation of the deposits, in the Sayak ore field.