Geochemical and mineralogical dispersal in till from the Mount Polley Cu-Au porphyry deposit, central British Columbia, Canada

The Quesnel terrane in the Interior Plateau of British Columbia, Canada, is highly prospective for locating new porphyry deposits; however, the bedrock in this region is obscured by a nearly continuous blanket of till, making mineral exploration challenging. Located within the Quesnel terrane is the Mount Polley deposit. It is an alkaline, silica-undersaturated, Cu-Au porphyry deposit mined by Imperial Metals Corporation. Eighty-six basal till samples were collected for geochemical and mineralogical analyses in the region of this deposit. Ore elements (Ag, Au and Cu), as well as pathfinder element (Hg and Zn) contents in till reflect detrital glacial dispersal from the Mount Polley deposit. The distribution of anomalous mineral counts of andradite garnet, apatite, chalcopyrite, epidote, jarosite and native gold also reflect glacial dispersal from the deposit. Outcrop-scale ice-flow indicators indicate a dominant ice-flow event to the NW that was preceded by a southwestward glacial advance. The element and mineral signatures of the Mount Polley Cu-Au porphyry deposit are dispersed in sub-glacial surface tills up to 12 km in the down-ice (NW) direction. We demonstrate that till geochemistry and mineralogy can serve for mineral exploration of Cu-Au porphyry mineralization in drift covered areas.

加拿大不列颠哥伦比亚省内陆高原（Interior Plateau）的奎斯内尔地体（Quesnel terrane）具有极高的找矿潜力，有望发现新的斑岩型矿床（porphyry deposits）；但该区域的基岩被近乎连续的冰碛物（till）盖层所覆盖，给矿产勘查带来了极大挑战。坐落于奎斯内尔地体范围内的波尔梅山矿床（Mount Polley deposit），是由帝国金属公司（Imperial Metals Corporation）开采的碱性、硅不饱和型铜金斑岩矿床。研究团队在该矿床周边区域采集了86件基底冰碛物样品，用于地球化学与矿物学分析。冰碛物中的成矿元素（Ag、Au、Cu）以及找矿指示元素（pathfinder element，Hg、Zn）的含量分布，均反映出源自波尔梅山矿床的冰碛碎屑分散特征。钙铁榴石（andradite garnet）、磷灰石（apatite）、黄铜矿（chalcopyrite）、绿帘石（epidote）、黄钾铁矾（jarosite）以及自然金（native gold）的异常矿物计数分布，同样反映出该矿床的冰川分散信号。露头尺度的冰流指示标志显示，区域内存在一次主导性的西北向冰流事件，其前期曾发生过西南向的冰川推进。波尔梅山铜金斑岩矿床的元素与矿物异常信号，在冰下表层冰碛物（sub-glacial surface tills）中沿顺冰流（西北向）方向最远可扩散至12公里范围。本研究证实，冰碛物的地球化学与矿物学特征，可用于漂移覆盖区（drift covered areas）内铜金斑岩型矿化的矿产勘查。