The chloride source of atacamite mineralization at the Radomiro Tomic porphyry copper deposit in northern Chile and the connection to regional geological evolution of northern South America.

摘要

The Radomiro Tomic porphyry copper deposit is located in the Atacama desert of northern Chile, 150 kilometers northeast of the city of Antofagasta. At Radomiro Tomic the principal ore is a copper-chloride mineral named atacamite, (Cu₄Cl₂(OH)₆) which is present in a large supergene oxide ore zone overlying more traditional copper sulfide enrichment.; Unmineralized, biotite-bearing, whole rock protore samples from the Radomiro Tomic deposit conform to typical low total bromine, (2 ppm) and heavy chlorine isotopes (δ37Cl = 0.1 to 2.5‰) values for igneous rocks. In contrast, elevated bromine contents, (22 to 180 ppm Br) and lighter δ37Cl values near 0.0‰ for the atacamite mineralization at Radomiro Tomic are clearly indicative of a non-magmatic origin for the mineralizing chloride.; Once the source of the introduced chloride was determined to be the upper Jurassic sediments, an investigation regarding the formation and distribution of the evaporite-bearing lithologies was undertaken.; Using published geological maps for northern Chile, Argentina, and southwestern Bolivia we subsequently compiled a series of maps at 2 million year intervals spanning the early Jurassic to the Mid-Miocene times (206–10 Ma). From these time slices a geological animation was created showing the spatial and temporal evolution of regional sedimentary basins as well as the migration of the Andean magmatic arc responsible for porphyry copper deposit genesis.; The major development during the Jurassic period was the formation of the Domeyko back-arc basin in which shallow marine sediments reflecting five marine transgressive events (206 Ma, 190 Ma, 176 Ma, 186 Ma, and 151 Ma) were deposited. Four intervening regressive events (197 Ma, 182 Ma, 170 Ma, and 155 Ma) are also recorded in the basin sediments, with the final event at 155 Ma responsible for the basin-wide deposition of massive evaporite sequences of the Millionaria formation.; Tertiary evolution saw four compressional uplift events (58 Ma, 38 Ma, 25–23 Ma, and ∼10 Ma), the initial formation of the Bolivian Altiplano, and the continued eastward migration of the magmatic arc. Of major importance was the emplacement of late Eocene to early Oligocene (36–34 Ma) magmatic bodies which would later become some of the world's largest copper deposit including Radomiro Tomic, Chuquicamata, El Salvador, and La Escondida.; Spatial and temporal visualizations models allow for the genesis of various lithologies and their interactions with subsequent magmatic systems to be investigated and possibly related to continental scale tectonic events. (Abstract shortened by UMI.)