The super-giant Oyu Tolgoi porphyry copper-gold deposits in the South Gobi
desert, Mongolia, consist of multiple discrete porphyry centers aligned within a north-northeast trending, >6.5 km long, arc-transverse mineralized corridor. The porphyries are linked to a tectono-magmatic event at ~372 Ma within a Devonian to Carboniferous volcanic arc, and U-Pb (zircon) geochronology records magmatic activity from ~390 Ma to ~320 Ma. The Oyu Tolgoi district underwent at least three discrete periods of syn- to post-mineral shortening and there is evidence for at least three unconformities within the Paleozoic sequence. Although the deposits were formed in an active orogenic
environment characterized by rapid uplift, their preservation is a reflection of climactic effects as well insulation from erosion by rapid burial under mass-wasted and pyroclastic material in the volcaniclastic apron of late-mineral dacitic volcanoes.
The porphyry copper-gold deposits are spatially and temporally related to
medium- to high-K calc-alkaline quartz monzodiorite (~372 Ma) and granodiorite (~366
Ma) intrusive phases that comprise the Late Devonian Oyu Tolgoi Igneous Complex
(OTIC). Adakite-like wholerock compositions as well as zircon grains with high
CeN/CeN*, EuN/EuN* and Yb/Gd in the sample populations from syn- and late-mineral
porphyry intrusions are different from younger intrusions that are not related to porphyry Cu-Au deposit formation. Moreover, mixed zircon populations within OTIC intrusions indicate that efficient assimilation of material from different host rocks by a convecting magma chamber occurred.
Mafic to intermediate volcanic units evolved from tholeiitic to calc-alkaline compositions, which is interpreted to be a reflection of marine arc maturation and
thickening. Felsic rock suites are dominantly high-K calc-alkaline, regardless of age.
Nd-isotopic geochemistry from all suites is consistent with magma derivation from
depleted mantle in an intra-oceanic volcanic arc and lead isotopic compositions indicate
that the sulfides in the porphyry Cu-Au deposits are genetically linked to the Late
Devonian magmas.
Magma mixing, adakite-like magmatism and rapid uplift and erosion in a juvenile
marine arc setting differentiate the ore-stage geologic environment at Oyu Tolgoi from other settings in active and fossil volcanic arcs.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU./2760 |
| Date | 05 1900 |
| Creators | Wainwright, Alan John |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | 10315021 bytes, application/pdf |
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