Polymetallic mineralised veins in ferroan/A-type Cretaceous leucogranite, Stewart Island, New Zealand

The 140 ± 1 Ma hypersolvus, ferroan, weakly peralkaline to weakly peraluminous North Red Head leucogranite in northwest Stewart Island is cut by quartz-pyrite-rich veins that contain a wide variety of Mo, Ag, Te, Bi, Au, Co, Cu, Pb, Zn, REE, Nb, Y, Th, U, Zr, Ti, Be and F-bearing minerals. Patchy hematite-pyrite alteration locally overprints leucogranite in the vicinity of the mineralised veins. Individual veins are up to 5 m thick and 200+ m long. U–Pb dating and trace-element geochemistry indicate a direct link between leucogranite crystallisation and exsolution of the vein-forming hydrothermal fluid. Mineralised veins developed along transpressional faults within the leucogranite soon after emplacement. Incipiently mineralised quartz ± pyrite veins at Waituna Bay and the northern end of West Ruggedy Beach several kilometres from North Red Head are probably part of the same hydrothermal system as the veins at North Red Head. Metal and alteration assemblages at North Red Head most closely resemble those in rare hydrothermal systems associated with oxidised fluorine-rich A-type granites.

位于斯图尔特岛西北部的北红头（North Red Head）淡色花岗岩形成于140±1 Ma，属过溶型、铁质、弱过碱至弱过铝质花岗岩，被富石英黄铁矿脉切割；这些脉体中产出多种含Mo、Ag、Te、Bi、Au、Co、Cu、Pb、Zn、稀土元素（REE）、Nb、Y、Th、U、Zr、Ti、Be及氟的矿物。在矿化脉体附近，斑块状赤铁矿-黄铁矿蚀变局部叠加于淡色花岗岩之上。单条脉体最大厚度可达5米，长度超200米。铀-铅（U-Pb）测年与微量元素地球化学研究表明，淡色花岗岩结晶与成脉热液流体的出溶存在直接关联。矿化脉体形成于淡色花岗岩侵位后不久的内部压扭断层沿线。距离北红头数公里外的怀图纳湾与西拉格迪海滩北端，产出初期矿化的石英±黄铁矿脉，其大概率与北红头的脉体属于同一热液系统。北红头的金属与蚀变组合，与罕见的富氧化氟A型（A-type）花岗岩相关热液系统最为相似。