玻利维亚塞德里克银矿床研究新进展

New Research Progress on Cerro Rico Deposit in Bolivia

塞德里克(Cerro Rico)银矿床位于玻利维亚的波托西省,是世界上最大的银矿床。矿床赋存在页岩区内,产生矿化作用的主要岩石是流纹英安岩岩体,其地表分布面积为1 700m×1 200m,在500m深处缩小至100m×100m。该银矿有多种类型的矿化作用,但最重要的是脉状矿化。矿区内2个流纹岩岩穹和1套熔结凝灰岩中的透长石和黑云母的40 Ar/39 Ar测年结果表明,银矿是在与岩浆有关的热液活动时期形成的,这段时期开始于(13.77±0.03)Ma,并持续了至少0.2Ma。明矾石的K-Ar测年结果显示表生氧化作用开始于13.5Ma,断续地持续了7.5Ma。研究区内流纹英安岩主量元素的分布清楚地反映了交代作用带的层次性,交代作用的全部发展过程涉及的空间范围大,时间长。微量元素的分布显示出F-V-Ga-Be-B-Cu-Nb-Sr-Pb-Zr-Sn-Co-Ba的元素沉淀顺序。

Cerro Rico is the world＇s largest silver deposit. The deposit was hosted in shale region, and the main rock which generates mineralization is rhyedacit porphyry body. Its surface distribution area is 1 700 m× 1 200 m, and reduced to 100 mN 100 m at a depth of 500 meters. Vein-hosted mineral deposit is the most important ore-deposit form, although other various styles of mineralization are present. High precision 40 Ar/39 Ar dating of sanidine and biotite from two rhyolitic domes and one ignimbrite suggests that the Cerro Rico was emplaced during a protracted period of magma-related hydrothermal activity beginning at （13.77±0.03） Ma and lasted for at least 0.2 Ma. K-Ar dating of alunite indicates that the supergene oxidation began around 13.5 Ma ago, and progressed semicontinuously for at least 7.5 Ma. The distribution of the major elements of the rhyedacit clearly reflects the level of metasomatism whose development process involves both large spatial extent and long time. The distribution of trace elements shows sequence of elements precipitatation is F-V-Ga-Be-B-Cu-Nb-Sr-Pb-Zr-Sn-Co-Ba.