The 9 Mile Deposit of the Barama-Mazaruni Greenstone Belt of the Guiana Shield: geochemistry, geochronology and regional significance

ABSTRACT: The granitoid and greenstone-hosted 9 Mile Deposit, located in the Paleoproterozoic Barama-Mazaruni Greenstone Belt of the Guiana Shield, is one of a series of gold deposits within the NW-SE trending Makapa-Kuribrong Shear Zone (MKSZ), which extends from Venezuela, through Guyana, and French Guiana. The 9 Mile Deposit is underlain by the upper section of a shallowly-dipping meta-rhyolite rock, which was intruded by a host granodiorite and subsequently intruded by of a series of mafic dykes. Auriferous quartz veins are associated with the NE-SW thrust which was crosscut by a steep E-W shear zone, at least 12 km in length. Field relationships and lithogeochemical data suggest that the granodiorite was crustally derived and emplaced in a volcanic arc or syn- to late-collisional setting. U-Pb (SHRIMP II) dating of zircons indicates the granodiorite intruded at approximately 2.15, Ga suggesting it is a local representative of a regional suite of syn- to late-tectonic granitoid plutons emplaced during the main phase of Trans-Amazonian Orogeny.摘要：赋存于花岗岩类与绿岩中的9英里矿床，地处圭亚那地盾（Guiana Shield）的古元古代（Paleoproterozoic）巴拉马-马扎鲁尼绿岩带（Barama-Mazaruni Greenstone Belt）内，属于北西-南东走向的马卡帕-库里布隆剪切带（Makapa-Kuribrong Shear Zone, MKSZ）所控制的一系列金矿床之一；该剪切带展布范围从委内瑞拉出发，经圭亚那延伸至法属圭亚那。9英里矿床的基底为一套缓倾变质流纹岩（meta-rhyolite），该套岩石先被花岗闪长岩（granodiorite）侵入，后续又被一系列镁铁质岩脉（mafic dykes）贯入。含金石英脉（auriferous quartz veins）与北东-南西向逆冲断层伴生，该逆冲断层被一条长至少12 km的陡立东西向剪切带切割。野外地质关系与岩石地球化学数据显示，该花岗闪长岩为壳源成因，形成于火山弧环境或同碰撞至碰撞晚期构造背景。对锆石进行的U-Pb（SHRIMP II）定年结果表明，花岗闪长岩的侵位时代约为2.15 Ga，这意味着其是跨亚马逊造山运动（Trans-Amazonian Orogeny）主阶段形成的一套区域同构造至后构造花岗岩类岩体的局部代表性岩体。