246 Economic Geology (Posters)

Wednesday, 3 November 2010
8:00 AM - 6:00 PM
Hall D

HELIUM AND ARGON ISOTOPE SYSTEMATICS IN FLUID INCLUSIONS OF THE BASE METAL ORE DEPOSITS, SOUTH KOREA

Paper number: 246-9
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Helium (3He/4He) and argon (40Ar/36Ar) isotopic ratios in ores from the base metal mineral deposits, South Korea were analyzed to investigate the magmatic contribution to ore forming fluids. Noble gases trapped in fluid inclusions in ore quartz and pyrite have a wide isotopic range from 0.17 to 4.12 RA (1RA = 1.40 ×10-6 Cm2STP/g) in 3He/4He for the Au-Ag mineral deposits, from 0.37 to 6.24RA for Pb-Zn-Cu mineral deposits and from 0.01 to 4.28RA for W-Mo ore deposits, respectively. It is noteworthy that the Sunshin epithermal gold deposits among the hydrothermal base metal ore deposits have unusually high helium isotopic ratios ranging from 2.4 to 4.1RA which is overlapped the value of mantle xenoliths (3.5 to 7.9 RA in 3He/4He) in the Korean peninsula. Mantle helium with high helium isotopic ratios were identified from fluid inclusions in auriferous quartz veins of epithermal Au-Ag ore deposits which are characterized by low sulfidation (adularia-sericite) type. It provides direct evidence of low sulfidation ore fluids in epithermal gold deposits links to magma from the mantle source.

The relatively high and wide 3He/4He ratios for Pb-Zn-Cu and W-Mo ores suggest that the ore forming fluids of base metal ore deposits were derived from the mantle sources, but were further diluted by air-saturated meteoric water and crustal helium contaminaton. However, the 3He/4He ratios ranging from 0.006 to 0.038 RA for Chongyang, Daewha and Wolak W- Mo ore deposits are similar to those of the crustal materials less than 0.02RA of 3He/4He due to the radiogenic 4He generated by the crustal U(Th).

The 40Ar/36Ar ratios in the Au-Ag ore forming fluids have extremely wide ranges from12913 to 299, reflecting the age of mineralization in each mineral deposit.

He-Ar isotopic signatures show that the base metal mineralization is closely related to Mesozoic igneous activities in South Korea. The coincidence of mantle derived He and Ar in the hydrothermal ore fluids of the base metal mineral deposits in South Korea is strong evidence that the ore fluids were formed by intrinsic mantle melting with crustal mixing during the Mesozoic granitic magmatism.