Publication Type:

Journal Article

Authors:

Barnes, Stephen J.; Mungall, James E.; Le Vaillant, Margaux; Godel, Belinda; Lesher, C. Michael; Holwell, David; Lightfoot, Peter C.; Krivolutskaya, Nadya; Wei, Bo

Source:

American MineralogistAmerican Mineralogist, Mineralogical Society of America, Washington, DC, United States, Volume 102, Number 3, p.473-506 (2017)

ISBN:

0003-004X

Keywords:

Africa, Asia, Australasia, australia, Canada, China, Commonwealth of Independent States, copper ores, copper sulfides, cumulates, eastern canada, Europe, Far East, Finland, igneous rocks, intrusions, KOMATIITE, Krasnoyarsk Russian Federation, Labrador, layered intrusions, metal ores, metals, mineral deposits, genesis, Newfoundland and Labrador, nickel ores, nickel sulfides, Norilsk region, Ontario, peridotites, petrography, platinum group, platinum ores, plutonic rocks, poikilitic texture, Precambrian, Russian Federation, Scandinavia, South Africa, Southern Africa, Stillwater Complex, Sudbury Igneous Complex, sulfides, Taymyr Dolgan-Nenets Russian Federation, textures, ultramafics, Voisey's Bay Deposit, volcanic rocks, Western Australia, Western Europe

Abstract:

A large proportion of ores in magmatic sulfide deposits consist of mixtures of cumulus silicate minerals, sulfide liquid, and silicate melt, with characteristic textural relationships that provide essential clues to their origin. Within silicate-sulfide cumulates, there is a range of sulfide abundance in magmatic-textured silicate-sulfide ores between ores with up to about five modal percent sulfides, called "disseminated ores," and "net-textured" (or "matrix") ores containing about 30 to 70 modal percent sulfide forming continuous networks enclosing cumulus silicates. Disseminated ores in cumulates have various textural types relating to the presence or absence of trapped interstitial silicate melt and (rarely) vapor bubbles. Spherical or oblate spherical globules with smooth menisci, as in the Black Swan disseminated ores, are associated with silicate-filled cavities interpreted as amygdales or segregation vesicles. More irregular globules lacking internal differentiation and having partially facetted margins are interpreted as entrainment of previously segregated, partially solidified sulfide. There is a textural continuum between various types of disseminated and net-textured ores, intermediate types commonly taking the form of "patchy net-textured ores" containing sulfide-rich and sulfide-poor domains at centimeter to decimeter scale. These textures are ascribed primarily to the process of sulfide percolation, itself triggered by the process of competitive wetting whereby the silicate melt preferentially wets silicate crystal surfaces. The process is self-reinforcing as sulfide migration causes sulfide networks to grow by coalescence, with a larger rise height and hence a greater gravitational driving force for percolation and silicate melt displacement. Many of the textural variants catalogued here, including poikilitic or leopard-textured ores, can be explained in these terms. Additional complexity is added by factors such as the presence of oikocrysts and segregation of sulfide liquid during strain-rate dependent thixotropic behavior of partially consolidated cumulates. Integrated textural and geochemical studies are critical to full understanding of ore-forming systems.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2017-043449<br/>Black Swan Deposit<br/>Insizwa Deposit<br/>Katinniq Deposit<br/>Kevitsa Intrusion<br/>Piaohechuan Deposit<br/>Raglan Belt<br/>Talnakh Deposit