Stable isotope geochemistry of the Archean Val-d'Or (Canada) orogenic gold vein field

A systematic study of the auriferous quartz veins of the Val-d'Or vein field, Abitibi, Quebec, Canada, demonstrates that the C, O, S isotope composition of silicate, carbonate, borate, oxide, tungstate and sulphide minerals have a range in composition comparable to that previously determined for the whole Superior Province. The oxygen isotope composition of quartz from early quartz - carbonate auriferous veins ranges from 9.4 parts per thousand to 14.4 parts per thousand whereas later quartz-tourmaline-carbonate veins have delta(18)O(quartz) values ranging from 9.2 parts per thousand to 13.8 parts per thousand. Quartz-carbonate veins have carbonate (delta(18)O: 6.9 - 12.5 parts per thousand; delta(13)C: - 6.2 - -1.9 parts per thousand) and pyrite (delta(34)S: 1.2 and 1.9 parts per thousand) isotope compositions comparable to those of quartz-tourmaline-carbonate veins (delta(18)O: 7.9 - 11.7 parts per thousand; delta(13)C: - 8.0 - - 2.4 parts per thousand; delta(34)S: 0.6 - 6.0 parts per thousand). delta(18)O(quartz) values in quartz-tourmaline-carbonate veins have a variance comparable to analytical uncertainty at the scale of one locality, irrespective of the type of structure, the texture of the quartz or its position along strike, across strike or down-dip a vein. In contrast, the oxygen isotope composition of quartz in quartz-tourmaline-carbonate veins displays a regional distribution with higher delta(18)O values in the south-central part of the vein field near the Cadillac Tectonic Zone, and which delta(18)O values decrease regularly towards the north. Another zone of high delta(18)O values in the northeast corner of the region and along the trace of the Senneville Fault is separated by a valley of lower delta(18)O values from the higher values near the Cadillac Tectonic Zone. Oxygen isotope isopleths cut across lithological contacts and tectonic structures. This regional pattern in quartz-tourmaline-carbonate veins is interpreted to be a product of reaction with country rocks and mixing between (1) a deep-seated hydrothermal fluid of metamorphic origin with minimum delta(18)O = 8.5 parts per thousand, delta(13)C = 0.6 parts per thousand and delta(34)S = - 0.4 parts per thousand, and ( 2) a supracrustal fluid, most likely Archean seawater with a long history of water-rock exchange and with maximum delta(18)O = 3.9 parts per thousand, delta(13) C = - 5.6 parts per thousand and delta(34)S = 5.0 parts per thousand.