ISBN:

0010-7999

Keywords:

absolute age, alkaline earth metals, Asia, basalts, chemical composition, chemical ratios, China, dates, dikes, Emeishan Basalts, Far East, flood basalts, gabbros, geochemistry, ICP mass spectra, igneous rocks, intrusions, ion probe data, isotope ratios, Isotopes, lamprophyres, large igneous provinces, layered intrusions, mafic composition, magma contamination, magmas, magmatic differentiation, magmatism, mantle, mantle plumes, mass spectra, metals, mineral composition, Nd-144/Nd-143, neodymium, nesosilicates, Ordovician, orthopyroxenite, orthosilicates, Paleozoic, patterns, Permian, petrography, plutonic rocks, pyroxenite, rare earths, SHRIMP data, silicates, spectra, Sr-87/Sr-86, Stable isotopes, strontium, Th/U, Trace elements, ultramafic composition, ultramafics, volcanic rocks, VOLCANISM, Yangtze Platform, zircon, zircon group

Abstract:

The approximately 260 Ma Baimazhai mafic-ultramafic intrusion is considered to be part of the Emeishan large igneous province and consists of orthopyroxenite surrounded by websterite and gabbro. The intrusion is variably mineralised with a massive sulphide ore body ( approximately 20 vol.%) in the core of the intrusion. Silicate rocks have Ni/Cu ratios ranging from 0.3 to 46 with majority less than 7 and are rich in LREE relative to HREE and show Nb and Ta anomalies in primitive mantle-normalized trace element patterns, with low Nb/Th (1.0-4.5) and Nb/La (0.3-1.0) ratios. Their epsilon (sub Nd(t)) values range from -3.3 to -8.4. Uniform Pd/Pt (0.73-5) and Cu/Pd (100,000-400,000) ratios throughout the intrusion indicate that all the sulphides in the rocks were formed in a single sulphide-saturation event. Modelling suggests that the Baimazhai rocks were formed when an Mg-rich magma became crustally contaminated in a deep-seated staging chamber. Crustal contamination (up to approximately 35%) drove the magma to S-saturation and forced orthopyroxene (opx) onto the liquidus. The crystal-bearing magma forced out of the staging chamber was migrated by flow differentiation and consequently, the denser sulphide melt and the opx crystals became centrally disposed in the flowing magma to form the Baimazhai intrusion.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2007-010701<br/>Baimazhai Intrusion