Evolution of the Giant Marcona-Mina Justa Iron Oxide-Copper-Gold District, South-Central Peru
Evolution of the Giant Marcona-Mina Justa Iron Oxide-Copper-Gold District, South-Central Peru
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DOI：
10.2113/gsecongeo.105.1.155
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发表时间：
2010-01-01
期刊：
影响因子：
5.8
通讯作者：
Moody, Timothy C.
中科院分区：
文献类型：
--
作者：
Chen, Huayong;Clark, Alan H.;Moody, Timothy C.
秘鲁中南部沿海的中生代氧化铁-铜-金矿亚省位于北纬15°11‘S，西经75°6’，与安第斯山脉中部著名的铁氧化物矿床马可纳(1.9GT@55.4%Fe)和米纳胡斯塔(Mina Justa)有关，后者是安第斯山脉IOCG中为数不多的主要铜矿之一，铜矿品位为346.6 Mt@0.71%。不经济的铜品位(平均0.12%)磁铁矿矿体在Marcona的侵位受横穿中侏罗世(Aalenian-Oxfordian)活动安山期-英安岩-浅海弧段的北东向断裂控制。相反，米纳朱斯塔的次生硫化物(类似于15g/tAg，0.12g/tAn)矿化是在白垩纪中期板块边界平行的阿普天-阿尔比卡内特盆地的反转过程中沿重新激活的斜纹-正向滑脱断裂侵位的，伴随着最早的、主要是花岗闪长-闪长岩的海岸基岩群。在Ar-49/Ar-39年代学的支持下，黑云母、金云母、阳起石、紫云母和钾长石的蚀变和矿化组合揭示了岩浆和热液作用的历史，从177 Ma到95 Ma，至少持续了80英里，其中富金属矿化事件发生在之前，并被贫化蚀变幕分开。分别在Aalenian(177 Ma)和Bajocian(171 Ma)产生了前驱体Marcona，海底热水活动早先变质的下古生界马可纳组硅质碎屑岩高温镁铁交代形成的斜方辉石和金云母-磁铁矿组合，以及新生的里奥格兰德组大火下的少量碳酸盐单元。随后广泛分布的钠长石-闪锌矿蚀变(钠-氯交代作用)在很大程度上早于但与一梯队块状磁铁矿矿体的侵位重叠，被次级磁铁矿-硫化物组合撕裂叠加。磁铁矿和弱的铜锌硫化物成矿作用与156~162 Ma的安山期喷发和英安岩侵入相吻合，终止了生长或弧形，但主要赋存于富石英的变碎屑岩中。162~159 Ma，氧化铁矿化由磁铁矿-黑云母-钙角闪石-金云母-氟磷灰石演化为磁铁矿-金云母-钙角闪石-磁黄铁矿-黄铁矿组合。它们在156~159 Ma被黄铜矿-黄铁矿-方解石+/-磁黄铁矿+/-闪锌矿方铅矿组合叠加，局部产生0.45%的铜和0.5%的锌。此后热液活动集中在马可纳东北3-4公里的米纳-朱斯塔地区，那里的中侏罗世安山岩在约157 Ma经历了强烈的钠长-阳起岩蚀变，即与马可纳的硫化物成矿作用和Ea的磁铁矿-微斜蚀变(K-Fe交代)同步。142毫安。然而，Mina Instil铜(银)矿床本身的开发开始得更晚，先后在109 Ma左右发生了光化作用，方解石沉积在镜面赤铁矿中，现在完全被磁铁矿假象，并在101~104 Ma之间交代侵位了贫瘠的块状磁铁矿和黄铁矿。最后，在95~99 Ma期间，黄铜矿-斑铜矿-闪长铜矿-辉铜矿成矿，含丰富的方解石和赤铁矿，呈长约400米、宽约200米的缓倾斜板状角砾岩和网状排列，以原有的磁铁矿-黄铁矿透镜体为核心。表生氧化作用在9.13 Ma+/-0.25 Ma的流纹安质褐辉岩流喷发前，形成了一条金粒陨石-凹凸棒石-金银金矿带，相当于铜矿储量的40%。虽然马可尼地区的主要磁铁矿和富铜中心在区域上是连续的，但它们记录了在时代上广泛分离的独立的成矿作用。此外，贫铜磁铁矿化Marcona是中侏罗世弧末喷发不可或缺的组成部分，代表了智利北部上新世El Laco磁铁矿矿床的浅海类似物，而Mina Justa铜硫化物矿体--与安第斯山脉中部其他经济的、中白垩世、富铜的IOCG矿床--如Candelaria-Punta del Cobre、Mantoverde和Raul-Consteable一样，是弧后火山沉积盆地版本中卤水释放的产物。与其他地方类似的造山环境一样，后一种环境在中生代安第斯山脉周期性地出现，长期的热液蚀变和矿化历史包含了许多贫瘠的事件，因此可能代表着IOCG的一个显著特征。存款氏族。
The Mesozoic iron oxide-copper-gold (IOCG) subprovince of littoral south-central Peru, centered fa latitude 15 degrees 11'S, longitude 75 degrees 6'W, incorporates Marcona, the preeminent central Andean iron oxide deposit (1.9 Gt @ 55.4% Fe), and Mina Justa, one of the few major Andean IOCG: deposits with economic copper grades (346.6 Mt @ 0.71% Cu). The emplacement of magnetite orebodies with uneconomic Cu grades (avg 0.12%) at Marcona was controlled by northeast-striking faults transecting an active andesitic-dacitic, shallow-marine Middle Jurassic (Aalenian to Oxfordian) arc. In contrast, hypogene Cu sulfide (similar to 15 g/t Ag, 0.12 g/t An) mineralization at Mina Justa was emplaced along reactivated listric-normal detachment faults during the mid-Cretaceous inversion of die contiguous, plate boundary-parallel, Aptian to Albian Canete basin, accompanied by the earliest, largely granodioritic-dioritic, stocks of the Coastal batholith. Alteration and mineralization assemblages, supported by Ar-49/Ar-39 geochronology of biotite, phlogopite, actinolite, cummingtonite, and K-feldspars, reveal a history of magmatic and hydrothermal processes extending episodically for at least 80 m.y., from ca. 177 to 95 Ma, wherein metal-rich mineralization events were preceded and separated by episodes of barren alteration.A Marcona, precursor, subocean-floor hydrothermal activity in the Aalenian (177 Ma) and Bajocian (171 Ma) generated, respectively, cummingtonite and phlogopite-magnetite assemblages through high-temperature Mg-Fe metasomatism of previously metamorphosed Lower Paleozoic Marcona Formation siliciclastic rocks and minor carbonate units underlying the nascent Rio Grande Formation fire. Subsequent areally widespread, albite-marialite alteration (Na-Cl metasomatism) largely predated but overlapped with the emplacement of an en echelon swarm of massive magnetite orebodies, in torn overprinted by subordinate magnetite-sulfide assemblages. Magnetite and weak Cu and Zn sulfide mineralization coincided with a 156 to 162 Ma episode of andesitic eruption and dacitic intrusion which terminated the growth or the arc, but was hosted largely by quartz-rich metaclastic rocks. From 162 to 159 Ma, iron oxide mineralization evolved from magnetite-biotite-calcic amphibole phlogopite fluorapatite to magnetite-phlogopite-calcic amphibole-pyrrhotite-pyrite assemblages. These were overprinted at 156 to 159 Ma by chalcopyrite-pyrite-calcite +/- pyrrhotite +/- sphalerite galena assemblages, locally resulting in grades of 0.45 percent Cu and 0.5 percent Zn.Hydrothermal activity was thereafter focused in the Mina Justa area, 3 to 4 kin to the northeast of Marcona, where Middle Jurassic andesites experienced intense albite-actinolite alteration at ca. 157 Ma, i.e., contemporaneous with sulfide mineralization at Marcona, and magnetite-microcline alteration (K-Fe metasomatism) at ea. 142 Ma. Development of the Mina instil Cu (-Ag) deposit proper, however, began much later, with, successively, actinolitization at ca. 109 Ma, the deposition of calcite in id specular hematite, now entirely pseudomorphed by magnetite, and the metasomatic emplacement of bodies of barren, massive magnetite and pyrite at 101 to 104 Ma. Finally, at 95 to 99 Ma, chalcopyrite-bornite-digenite-chalcocite mineralization, with abundant calcite and hematite, was emplaced as two similar to 400-m-long, similar to 200-m-wide, gently dipping, tabular arrays of breccia and stockwork, cored by preexisting magnetite-pyrite lenses. Supergene oxidation generated a chrysocolla-atacamite-covellite blanket, hosting similar to 40 percent of the Cu reserve, prior to the eruption of a 9.13 +/- 0.25 Ma rhyodacitic ignimbrite flow.Although areally contiguous, the major magnetite and copper-rich centers of the Marconi district record independent it metallogenic episodes widely separated in age. Further, whereas the Cu-poor magnetite mineralization Marcona was integral to die terminal eruptions of the Middle Jurassic arc, representing a shalow-marine analog of the Pliocene El Laco magnetite deposits of northern Chile, the Mina Justa Cu sulfide orebodies-like the other economic, mid-Cretaceous, Cu-rich IOCG deposits of the central Andes, e.g., Candelaria-Punta del Cobre, Mantoverde, and Raul-Condestable-was the product of brines released during the in version of back-arc volcanosedimentary basins. The latter environment recurred episodically in tie Mesozoic Andes, as in comparable orogenic settings elsewhere, and extended histories of hydrothermal alteration and mineralization, incorporating numerous barren events, may therefore represent a salient feature of the IOCG. deposit clan.