Supergene enrichment of copper deposits since the onset of modern hyperaridity in the Atacama Desert,Chile |
| |
| Authors: | Martin Reich Carlos Palacios Gabriel Vargas Shangde Luo Eion M Cameron Matthew I Leybourne Miguel A Parada Alejandro Zúñiga Cheng-Feng You |
| |
| Institution: | 1.Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas,Universidad de Chile,Santiago,Chile;2.Earth Dynamic System Research Center & Department of Earth Sciences,National Cheng-Kung University,Tainan,Republic of China;3.Eion Cameron Geochemical Inc.,Carp,Canada;4.Ocean Exploration, GNS Science,Lower Hutt,New Zealand;5.Departamento de Ingeniería Mecánica, Facultad de Ciencias Físicas y Matemáticas,Universidad de Chile,Santiago,Chile |
| |
| Abstract: | Supergene enrichment of Cu deposits in the Atacama Desert has played a critical role in making this the prime Cu-producing
province of the world. Previously, this has been believed to have occurred exclusively over a long period from the middle
Eocene to the late Miocene, which ended when climatic conditions changed from arid to hyperarid. Here, we report U-series
disequilibrium ages in atacamite-bearing supergene assemblages that provide a new conceptualization on both the supergene
enrichment process and the onset of extreme hyperaridity in the Atacama Desert. 230Th–234U ages of gypsum intergrown with atacamite in supergene veins from Cu deposits cluster at ~240 ka (Chuquicamata), 130 ka (Mantos
Blancos, Spence), and 80 ka (Mantos de la Luna, Michilla). When coupled with previous data, these results indicate that supergene
enrichment of Cu deposits did not cease after the onset of hyperaridity. We propose that supergene enrichment in the Atacama
region developed in two main stages. The main phase, caused by downward circulation of meteoric waters in a semi-arid setting,
was active from 45 until ~9 Ma, with a last pulse ca. 5 Ma in the southern Atacama Desert. During this phase, atacamite-bearing
supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when
contacted by meteoric water. This was followed by a second stage starting at ~2–1.5 Ma and continuing until at least the late
Pleistocene, when deep formation waters derived from the basement passed up through and modified the pre-existing supergene
Cu oxide minerals. Atacamite has then been preserved in the prevailing hyperarid climate. |
| |
| Keywords: | Copper porphyry deposits Supergene enrichment U-series disequilibrium ages Atacamite Chile |
| 本文献已被 SpringerLink 等数据库收录！ |
|
