|
|||||
|
|
On the Initiation of Metamorphic Sulfide Anatexis |
|
| Authors: | Tomkins Andrew G; Pattison David R M; Frost B Ronald |
| Institution: | 1Department of Geology and Geophysics, University of Calgary, Calgary, AB, Canada T2N 1N4 2School of Geosciences, Monash University, PO Box 28E, VIC. 3800, Australia 3Department of Geology and Geophysics, University Of Wyoming, Laramie, WY 82071, USA |
| Abstract: | Mineral assemblages in common sulfide ore deposits are examinedtogether with phase relations to (1) investigate the pressure–temperatureconditions required for the onset of metamorphically inducedpartial melting involving economic minerals, and (2) place constraintson the amount of melt produced. Deposits that contain sulfosaltor telluride minerals may start to melt at conditions rangingfrom lowest greenschist facies to amphibolite facies. Depositslacking sulfosalt and/or telluride minerals may begin to meltonce P–T conditions reach the upper amphibolite facies,if galena is present, or well into the granulite facies if galenais absent. The result is two broad melting domains: a low- tomedium-temperature, low melt volume domain involving meltingof volumetrically minor sulfosalt and/or telluride minerals;and a high-temperature, potentially higher melt volume domaininvolving partial melting of the major sulfide minerals. Epithermalgold deposits, which are especially rich in sulfosalt minerals,are predicted to commence melting at the lowest temperaturesof all sulfide deposit types. Massive Pb–Zn (–Cu)deposits may start to melt in the lower to middle amphibolitefacies if pyrite and arsenopyrite coexist at these conditions,and in the upper amphibolite facies if they do not. Exceptingsulfosalt-bearing occurrences, massive Ni–Cu–PGE(platinum group element) deposits will show little to no meltingunder common crustal metamorphic conditions, whereas disseminatedCu deposits are typically incapable of generating melt untilthe granulite facies is reached, when partial melting commencesin bornite-bearing rocks. The volume of polymetallic melt thatcan be generated in most deposit types is therefore largelya function of the abundance of sulfosalt minerals. Even at granulite-faciesconditions, this volume is usually less than 0·5%. Theexception is massive Pb–Zn deposits, where melt volumessignificantly exceeding 0·5 vol. % may be segregatedinto sulfide magma dykes, allowing mobilization over large distances. KEY WORDS: sulfide melt; ore deposits; melt migration; metamorphism |
| Keywords: | : sulfide melt ore deposits melt migration metamorphism |
| 本文献已被 Oxford 等数据库收录！ | |