Magmatic Evolution of the Giant El Teniente Cu–Mo Deposit, Central Chile
Magmatic Evolution of the Giant El Teniente Cu–Mo Deposit, Central Chile
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DOI：
10.1093/petrology/egq029
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发表时间：
2011
影响因子：
3.9
通讯作者：
C. Stern;M. A. Skewes;Alejandra Arévalo
中科院分区：
文献类型：
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作者：
C. Stern;M. A. Skewes;Alejandra Arévalo
世界上最大的铜存款，是在晚中新世和上新世侵入更古老的Teniente火山杂岩（或Farellones Fm; 14·2^6·5 Ma）的岩体。该存款的晚中新世和上新世的深成容矿岩石依次包括较大的（450 km）Teniente镁铁质杂岩岩盖（8·9 ~ 1·4 Ma），较小（30 km）的休厄尔等粒英云闪长岩杂岩体（7·05 ~ 0·14 Ma）及伴生的安山岩床（8.20.5 ~ 6.60.4Ma），小的英安斑岩体（51 km; 6·09 0·18 Ma），异常的富Cu、S的含“斑岩A”型花岗岩体（51 km; 5·67 0·19 Ma），Teniente英安岩斑岩脉（51公里; 5·28 ~ 0·10 Ma），次安粗岩脉（4·82 0·09 Ma），最后形成一个小型英安岩侵入体（4·58 0·10 Ma），它们的同位素组成基本相似（Sr/Sr 1/4 0·7039 ^0·7042; eNd 1/4 ~ 2.5 ~ 2.3.5），也与Teniente火山杂岩喷出岩有关，但与更古老的晚渐新世至早中新世火山岩不同（Sr/Sr 1/4 0·7033 ^0·7039; eNd 1/4 0 3·8 ~ 6·2）和较年轻的上新世成矿后基性脉岩和熔岩（Sr/Sr 1/4 0·7041 ^0·7049; eNd 1/4 0 1·1 ~ 1·1）。多个铜矿化岩浆热液角砾岩筒与长英质斑岩侵入体同期侵位，至少在6·31 0·03 ~ 4·42 0·02 Ma之间，这些矿化角砾岩筒是由冷却岩体中岩浆流体出溶形成的，它们的根源在采矿和勘探钻探的最深处，与长英质斑岩来自同一个岩浆房，为了在存款中产生100 10吨的铜，需要岩基大小（4600 km）的岩浆量与100 ppm的铜。我们认为，无论是矿化的岩浆热液角砾岩和体积逐渐变小的更细分，但同位素相当，晚中新世和上新世长英质深成岩的主机存款来自一个大的，长寿的，热和化学分层，开放系统的岩浆房，或岩浆管道系统的屋顶，从下面的地幔来源的岩浆补给。只有当该系统完全固化后，成矿后镁铁质橄榄石-角闪石-层状岩脉（3·85 0·18 ~ 2·9 0·6 Ma）才从地幔穿过该系统到达地表。显著的渐进式时间同位素演化，（0·7033 ~ 0·7049）和较低的eNd（1966·2 ~ 1961·1）晚渐新世至上新世，在El Teniente附近形成的镁铁质幔源岩浆，并暗示了其次弧幔源区部分原因是大陆边缘被构造侵蚀的俯冲地壳增加了地幔源区的污染。矿化后的橄榄石-角闪石-层状岩也意味着上新世安第斯弧这一部分以下的地幔的广泛水合作用，这可能在产生富含氧化挥发分的岩浆和ElTeniente的矿化中发挥了作用。
ElTeniente, the world’s largest Cu deposit, is hosted in Late Miocene and Pliocene plutons that intrude the older Teniente Volcanic Complex (or Farellones Fm; 14·2^6·5 Ma). The Late Miocene and Pliocene plutonic host rocks of the deposit include, sequentially, the relatively large (450 km) Teniente Mafic Complex laccolith (8·9 1·4 Ma), the smaller ( 30 km) Sewell equigranular tonalite complex (7·05 0·14 Ma) and associated andesitic sills (8·2 0·5 to 6·6 0·4 Ma), small dacitic porphyry stocks (51km; 6·09 0·18 Ma), the unusual Cuand S-rich ‘Porphyry A’anhydrite-bearing granitoid stock (51km; 5·67 0·19 Ma), the Teniente Dacite Porphyry dike (51km; 5·28 0·10 Ma), minor latite dikes (4·82 0·09 Ma), and finally a small dacite intrusion (4·58 0·10 Ma).These plutonic rocks are all isotopically similar to each other (Sr/Sr1⁄4 0·7039^0·7042; eNd1⁄4þ2·5 to þ3·5) and also to the Teniente Volcanic Complex extrusive rocks, but distinct from both older Late Oligocene to Early Miocene volcanic rocks (Sr/Sr1⁄4 0·7033^0·7039; eNd1⁄4þ3·8 toþ 6·2) and younger Pliocene post-mineralization mafic dikes and lavas (Sr/Sr1⁄4 0·7041^0·7049; eNd1⁄4þ1·1 to 1·1). Multiple Cu-mineralized magmatic^hydrothermal breccia pipes were emplaced into these plutonic rocks during the same time period as the felsic porphyry intrusions, between at least 6·31 0·03 and 4·42 0·02 Ma.These mineralized breccia pipes, which formed by exsolution of magmatic fluids from cooling plutons, have their roots below the deepest level of mining and exploration drilling and were derived from the same magma chamber as the felsic porphyries, 44 km below the paleosurface.To produce the 100 10 tonnes of Cu in the deposit requires a batholith-size (4600 km) amount of magma with 100 ppm Cu. We suggest that both the mineralized magmatic^hydrothermal breccias and the progressively smaller volumes of more fractionated, but isotopically equivalent, Late Miocene and Pliocene felsic plutonic rocks that host the deposit were derived from the roof of a large, long-lived, thermally and chemically stratified, open-system magma chamber, or magmatic plumbing system, recharged from below by mantle-derived magmas. Only when this system fully solidified did post-mineralization mafic olivine-hornblende-lamprophyre dikes (3·85 0·18 to 2·9 0·6 Ma) pass through the system from the mantle to the surface. The significant progressive temporal isotopic evolution, to higher Sr/Sr (from 0·7033 to 0·7049) and lower eNd (from þ6·2 to 1·1), that occurred between the Late Oligocene and Pliocene in the vicinity of El Teniente for mafic mantle-derived magmas, and by implication their sub-arc mantle-source region, was due in part to increased mantle-source region contamination by subducted crust tectonically eroded off the continental margin. The post-mineralization olivine-hornblende-lamprophyres also imply extensive hydration of the mantle below this portion of the Andean arc by the Pliocene, which may have played a role in producing oxidized volatile-rich magmas and mineralization at ElTeniente.