Zircon U-Pb geochronology and geochemistry of the Cerro Colorado porphyry copper deposit, northern Chile
Zircon U-Pb geochronology and geochemistry of the Cerro Colorado porphyry copper deposit, northern Chile
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智利北部科罗拉多山斑岩铜矿床的锆石 U-Pb 年代学和地球化学
DOI：
10.1016/j.oregeorev.2017.12.019
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发表时间：
2018
影响因子：
3.3
通讯作者：
Tattitch Brian C.
中科院分区：
文献类型：
--
作者：
Tsang Debbie P.W.;Wallis Simon R.;Yamamoto Koshi;Takeuchi Makoto;Hidaka Hiroshi;Horie Kenji;Tattitch Brian C.
斑岩铜矿主要形成于与火山弧有关的会聚板块边缘。然而，它们与活火山作用的时间关系不太清楚。活跃的火山活动通常被认为会阻碍PCD的形成，一些工作者得出结论，PCD的形成必须发生在火山活动的平静期或火山活动的减弱阶段。然而，一些研究已经记录的证据表明，同喷发PCD的形成。通过放射性测年、地球化学研究和对来自Cerro科罗拉多PCD（必和必拓位于美国新泽西州的一处资产）的岩芯的观察，智利，提供了与同火山PCD形成在一个火山edigilation. Textureobservations在两个手标本和显微尺度结合新的LA-ICPMS和锆石SHRIMP定年的研究表明，塞罗科罗拉多地区的侵入历史可以分为两个主要单元：一个斑状英云闪长岩约1000米。53.5麻和斑状石英二长岩约。50马。也有证据表明，在约结晶。60 Ma，但没有识别出相应的明显岩性。石英斑岩单位以前确定为最年轻的侵入体被重新解释为二长岩的蚀变等价物。最年轻的侵入体为斑状花岗闪长岩，年龄为51-50 Ma。这些单元仅显示少量金属矿化，表明Cerro科罗拉多矿的主要矿化阶段发生在数百万年前，与两个主要的火成岩侵入脉冲相吻合，这与记录的Ar-Ar年龄一致。以往的研究报告的Re-Os年龄表明，早期阶段的矿化在约。56-54 Ma。对切取Cerro科罗拉多矿主岩的火山相关角砾岩中锆石的U-Pb测年显示，火山活动的一个阶段大约在1980年。57 Ma，区域白垩纪Cerro Empexa地层形成后。这一年龄范围与侵入斑岩单位的年龄重叠，表明火山活动与科罗拉多塞罗的成矿次火山侵入体之间存在密切的时间关系。活火山作用和矿化之间的联系得到了超细颗粒基质的加强，并且存在与二长岩-石英斑岩股票相关的强烈角砾岩，表明在侵位过程中发生了减压和挥发性释放。
Porphyry Copper Deposits (PCDs) dominantly form in convergent plate margins genetically related to volcanic arcs. However, their temporal relationships with active volcanism are less clear. Active volcanic activity is often considered to impede the formation of PCDs and some workers have concluded that PCD formation must take place at times of volcanic quiescence or at a waning stage of volcanism. However, several studies have documented evidence suggesting syn-eruption PCD formation. A combination of radiometric dating, geochemistry studies and observations of rock cores from the Cerro Colorado PCD, a BHP Billiton property located in N. Chile, provides evidence compatible with syn-volcanic PCD formation within a volcanic edifice.Textural observations at both hand specimen and microscopic scales combined with new LA-ICPMS and SHRIMP dating of zircons suggest the intrusive history of the Cerro Colorado area can be separated into two main units: a porphyritic tonalite ca. 53.5 Ma and a porphyritic quartz monzonite ca. 50 Ma. There is also evidence for crystallisation at ca. 60 Ma, but a corresponding distinct lithology was not identified. A quartz porphyry unit previously identified as the youngest intrusive body is reinterpreted as an altered equivalent of the monzonite. The youngest intrusive units are represented by porphyritic granodiorite with an age 51–50 Ma. These units only show minor metal mineralisation suggesting that the main phase of mineralisation in the Cerro Colorado mine occurred over a few million years, bracketed by the two main pulses of igneous intrusion, which are consistent with documented Ar–Ar ages. Re–Os ages reported by previous studies suggest an earlier phase of mineralisation at ca. 56–54 Ma. U–Pb dating of zircon from a volcanic-related breccia that cuts the host rocks of the Cerro Colorado Mine reveals a phase of volcanic activity at ca. 57 Ma, after formation of the regional Cretaceous Cerro Empexa Formation. This age range overlaps the ages derived for the intrusive porphyry units suggesting a close temporal relationship between volcanism and the ore-forming subvolcanic intrusions in Cerro Colorado. A link between active volcanism and mineralisation is reinforced by the ultrafine-grained matrix and the presence of strong brecciation associated with the monzonite-quartz porphyry stock suggesting decompression and volatile release have taken place during emplacement.