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Genesis of the exotic chrysocolla — “copper pitch/wad” — atacamite/brochantite ore at the Exótica (Mina Sur) deposit, Chuquicamata, Chile
Mineralium Deposita ( IF 4.8 ) Pub Date : 2022-11-09 , DOI: 10.1007/s00126-022-01147-7
Bernhard Dold, Marie-Caroline Pinget, Lluís Fontboté

Detailed mineralogical and textural studies, combined with sequential X-ray diffraction and geochemical modeling, helped to solve the “copper pitch/wad” enigma in the Exótica deposit located downstream of the Chuquicamata porphyry copper deposit. Copper pitch and copper wad are essentially chrysocolla with co-precipitated Mn oxides, mainly birnessite, as well as pseudo-amorphous Mn oxide/oxyhydroxides. Linking the mineralogical, geochemical, and textural evidences with the geological, tectonic, and climatic evolution of the Chuquicamata–Calama area, a four-step genetic model for the evolution of the Exótica deposit is presented: (A) formation of a mature supergene enrichment profile at Chuquicamata (~ 30–25 Ma to ~ 15 Ma) during an erosion-dominated regime (∼900 m of erosion) which was accompanied by acidic (pH ∼2–4) Cu-Mn-Si-dominated rock drainage (ARD) with fluid flow southwards through the Exótica valley towards the Calama Basin, resulting in a strongly kaolinized and chrysocolla/copper wad-impregnated bedrock of the Exótica deposit; (B) deposition of the Fortuna gravels in the Exótica valley (starting ∼19 Ma) intercepted the Cu-Mn-Si-dominated ARD, triggering the main chrysocolla, copper pitch/wad mineralization as syn-sedimentary mineralization by chiefly surficial flow in strongly altered gravels; (C) tectonic freezing and onset of hyper-aridity (∼15–11 Ma) exposed the enriched chalcocite blanket of Chuquicamata to oxidation, resulting in acidic (pH ~ 2–4) and Cu-Si-dominated solutions with less Mn. These solutions percolated in a slightly more reducing groundwater flow path and mineralized relatively unaltered gravels with pure chrysocolla; and (D) ingression of confined chloride-rich groundwater in the upper oxidation zone of Chuquicamata, most likely between 6 and 3 Ma, is responsible for the atacamite/brochantite mineralization (pH ~ 5.5–7) of mainly unaltered gravels in the northern and central part of the Exótica deposit.



中文翻译:

智利 Chuquicamata 的 Exótica (Mina Sur) 矿床中奇异金孔雀石的起源——“铜沥青/wad”

详细的矿物学和结构研究,结合连续 X 射线衍射和地球化学建模,有助于解开位于 Chuquicamata 斑岩铜矿下游的 Exótica 矿床中的“铜沥青/wad”之谜。铜沥青和铜絮本质上是金孔雀石与共沉淀的锰氧化物,主要是水钠锰矿,以及假无定形的锰氧化物/氢氧化物。将矿物学、地球化学和结构证据与 Chuquicamata-Calama 地区的地质、构造和气候演化联系起来,提出了 Exótica 矿床演化的四步成因模型:(A) 在以侵蚀为主的区域(侵蚀约 900 m)期间,Chuquicamata(约 30-25 Ma 至约 15 Ma)形成成熟的表生富集剖面,并伴有酸性(pH 约 2-4)Cu-以锰硅为主的岩石排水系统(ARD),流体通过 Exótica 山谷向南流向 Calama 盆地,导致 Exótica 矿床的基岩具有强烈的高岭土和金孔雀石/铜团浸渍;(B) Exótica 山谷中 Fortuna 砾石的沉积(从 ∼19 Ma 开始)截获了以 Cu-Mn-Si 为主的 ARD,触发了主要的金孔雀石、铜沥青/wad 矿化作为同沉积矿化,主要是强烈的地表流动蚀变砾石;(C)构造冻结和超干旱(~15-11 Ma)的开始使 Chuquicamata 富集的辉铜矿层暴露于氧化,导致酸性(pH ~ 2-4)和以Cu-Si为主的溶液,Mn较少。这些溶液渗入略微减少的地下水流动路径,并用纯金孔雀矿化相对未改变的砾石;(D) Chuquicamata 上部氧化带的封闭富含氯化物地下水的进入,最有可能在 6 到 3 Ma 之间,是北部主要未改变的砾石的铜矿/溴铜矿矿化 (pH ~ 5.5-7) 和Exótica 矿床的中部。

更新日期:2022-11-10
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