A petrological and geochronological study of a 360 Ma metallogenic event in Maritime Canada with implications for lithophile-metal mineralization in the Canadian Appalachians

作者：Kontak Daniel J^*; Horne Richard J; Creaser Robert A; Petrus Joseph A; Archibald Douglas

来源：Canadian Journal of Earth Sciences, 2013, 50(11): 1147-1163.

DOI：10.1139/cjes-2013-0019

The occurrence of ca. 360 Ma greisen-related molybdenite mineralization in the Clayton Hill biotite-muscovite leucomonzongranite (%26lt;1 km(2)) is unusual for the southwestern Meguma terrane of the Maritime Appalachians, where 380 Ma granite-related Sn mineralization dominates. The presence of extensive hornfelsing and occurrence of mineralized (Sn-W-Cu-Zn) skarns in the area suggests a larger intrusion occurs at depth. The intrusion and mineralization are constrained to 361 Ma based on concordant Re-Os (molybdenite) and Ar-40/Ar-39 (muscovite) ages, which equates to other ca. 360 Ma granites in the area, hence magmatism of this age is more widespread than previously considered. The intrusion is highly evolved (74 wt.% SiO2), metaluminous (A/CNK = 1-1.05; A/CNK = molar ratio [Al2O3/(CaO + Na2O + K2O)]) and depleted in cafemic and transition elements. Rare-earth elements (Sigma REE = 106-23 ppm) are strongly fractionated with light rare-earth elements (LREE) enriched (La/Lu-N = 10), and negative Eu anomalies. Biotite is Fe-rich (Fe/(Fe + Mg) = 0.75), and both biotite and muscovite are F deficient. These geochemical features indicate affinity to the other 360 Ma granites and suggest a similar petrogenesis with some A-type affinity. Mineralization occurs as molybdenite-bearing greisens and rusty miaroles lined with pyrite and enrichment in Cu-As-Bi-Au. Stable isotopes (O, S) indicate greisen formation at 450 degrees C from fluids with delta O-18(H2O) = 7 parts per thousand and delta S-34(H2S) = 2 parts per thousand-3 parts per thousand, which suggests an A- or I-type magmatic reservoir rather than a peraluminous magma. These data indicate the presence of a widespread magmatic event that is 20 Ma younger than the 380 Ma Sn-base metal event in southern Nova Scotia (e. g., East Kemptville). That this event is the same age as the world class Mount Pleasant Mo-Sn-W-Zn-In deposit of southern New Brunswick indicates additional potential for significant granite-related mineralization in this part of Atlantic Canada.

• 出版日期2013-11