加拿大Sullivan超大型Pb-Zn-Ag矿床中几个指示成矿环境的特征矿物研究

Ore-Forming Environmental Indicator Minerals from the Sullivan Giant Pb-Zn-Ag Ore Deposit, Canada

加拿大Sullivan矿床是世界上最典型的SEDEX型Pb Zn Ag矿床。对该矿床中产出的几个特征矿物 ,如硼矿物电气石 ,富氯的方柱石和黑云母 ,富钡的钾长石和白云母 ,及富锰的石榴子石、绿泥石、碳酸盐和钛铁矿进行了研究。指出这些矿物的存在反映了该矿床产出的物理化学环境。提出成矿流体可能淋滤了深部存在的非海相蒸发岩层 ,层状硫化物矿石可能形成于海底高盐度热卤水池中。

Sullivan Pb-Zn-Ag deposit (British Columbia, Canada) is a classic SEDE X-type massive sulfide deposit, which occurs conformably within clastic metased i mentary rocks of the Middle Proterozoic Aldridge Formation. Several typical mine rals from this deposit are studied, including B-rich (tourmaline), Cl-rich (sc apolite and biotite), Ba-rich (feldspar and mica), and Mn-rich (garnet, chlori te, carbonate and ilmenite) minerals. Tourmaline shows a wide variation of chemi cal compositions, from Mg-rich dravite to Fe-rich schorl and Ca-rich uvite. T he δ- 11B values of the tourmalines are from-11.1 to-2.9‰, which is si milar to the range (-15.4 to-1.7‰) found worldwide in tourmalines from mass ive sulfide deposits and tourmalinites in dominantly clastic metasedimentary ter ranes. Multiple stages of tourmaline formation are distinguished in the Sullivan deposit. Cl-rich scapolites occur in the bedded sulfide ores at Sullivan. The scapolite porphyro blasts are more Ca-rich (EqAn= 40.8～50.9) and Cl-poor (X Cl= 0.38～0.54) than t he fine-grained euhedral scapolite crystals (EqAn= 22.4～35.1 and X Cl= 0. 72～0.8 1) in the same sample. Cl-rich biotites are found only in the bedded sulfide or e s with 0.76 to 1.46 wt% Cl and a limited variation of Mg/(Mg+Fe) ratios (0.34～ 0.37). Other biotites are commonly Cl-poor (<0.2 wt%Cl) and have a wider range of Mg/(Mg+Fe) ratios (0.24～0.69). Ba-rich feldspar and muscovite with BaO up to 6.8 wt% also occur within the bedded sulfide ores in association with to urmaline, carbonates, and sulfides. Mn-rich garnets (up to 79% end-member spe ss artine) at Sullivan constitute coticules (spessartine-quartz rocks) and spessar t ine-rich tourmalinites; they also disseminated in sulfide ores and other countr y rocks. Other Mn-rich minerals include chlorite (up to 4.7 wt% MnO), carbonate s (up to 30 wt% MnO), and ilmenite (up to 16.7 wt% MnO). It is suggested that th e existences of aforementioned B-, Cl-, Ba-, and Mn-rich minerals at Sulliva n ar e indicative of possible non-marine evaporite involvement in the ore-forming s ys tem and the bedded sulfide ores were likely precipitated in a dense brine pool i n the Proterozoic sea floor at Sullivan.