Magmatic and hydrothermal quartz of the São Jorge gold deposit, Tapajós Gold Province, Pará: Petrography, scanning electron microscopy-cathodoluminescence and metallogenetic implications

Studies in crystals of quartz present in the mineral associations to the area of the São Jorge gold deposit, Tapajós Gold Province, southwest of the Pará state, identified four morphological and textural types (Qz1, Qz2, Qz3 and Qz4) by scanning electron microscopy-cathodoluminescence images. In the more preserved rocks of the Younger São Jorge Jovem granite, rich in amphibole and biotite (associations 1 and 2), anhedral crystals of magmatic quartz with high to moderate luminescence (Qz1) dominate. In the partly altered rocks (associations 2 and 3), post-magmatic to hydrothermal fluids affected the granite, and filled fractures in Qz1 and crystallized not luminescent (dark) Qz2. In the most intensely altered rocks (association 4), successive alteration, dissolution and recrystallization processes gave rise to typically hydrothermal zoned, subhedral (Qz3) and euhedral (Qz4) quartz crystals. Images by backscattered electrons and semiquantitative analysis by energy dispersive spectroscopy identified two generations of gold: Au1, enriched in Ag (4.3 to 23.7%) and associated to pyrite crystals; Au2, enriched in Te (1.1 to 17.2%) and included or associated to Qz4. The scanning electron microscopy-cathodoluminescence study provided important information that was preserved in the quartz structure. The morphological and textural evolution of this mineral in different stages shows the gradual action of the hydrothermalism in the rocks and minerals associations of São Jorge deposit. Gold mineralization of the deposit was chemically (energy dispersive spectroscopy) and paragenetically (pyrite, sphalerite and Qz4) characterized, and it can be divided into different generations or mineralizing events. The effectiveness of the methodology used in this study was established, allowing its application in studies of other hydrothermal deposits.

针对帕拉州西南部塔帕若斯金矿省（Tapajós Gold Province）圣若热金矿床矿物组合中产出的石英晶体开展研究，通过扫描电子显微镜-阴极发光（Scanning Electron Microscopy-Cathodoluminescence）成像分析，识别出四类形态与结构类型的石英（Qz1、Qz2、Qz3及Qz4）。在闪石与黑云母富集、保存较好的年轻圣若热花岗岩（São Jorge Jovem Granite）中（对应组合1与组合2），以发光强度中至高的他形岩浆石英（Qz1）为主。在发生部分蚀变的岩石中（对应组合2与组合3），岩浆期后至热液流体作用于花岗岩，充填于Qz1的裂隙内并结晶形成无发光（暗色）的Qz2。在蚀变程度最强的岩石中（对应组合4），历经多期蚀变、溶解与重结晶作用，形成典型热液分带的亚自形（Qz3）与自形（Qz4）石英晶体。通过背散射电子成像与能量色散光谱（Energy Dispersive Spectroscopy）半定量分析，识别出两期金矿物：其一为Au1，银含量介于4.3%~23.7%，与黄铁矿晶体共生；其二为Au2，碲含量介于1.1%~17.2%，包裹于Qz4中或与其共生。本次扫描电子显微镜-阴极发光研究获得的关键信息留存于石英的晶体结构中。该矿物在不同阶段的形态与结构演化，揭示了圣若热金矿床岩石与矿物组合中热液作用的渐进过程。该矿床的金矿化通过化学（能量色散光谱）与共生矿物组合（黄铁矿、闪锌矿与Qz4）手段完成了系统表征，可划分为多期成矿事件。本次研究所用方法的有效性得到验证，可推广应用于其他热液矿床的相关研究。