Petrogenesis of ore-forming and pre/post-ore granitoids from the Kounrad, Borly and Sayak porphyry/skarn Cu deposits, Central Kazakhstan
Petrogenesis of ore-forming and pre/post-ore granitoids from the Kounrad, Borly and Sayak porphyry/skarn Cu deposits, Central Kazakhstan
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DOI：
10.1016/j.gr.2015.10.005
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发表时间：
2016-09
影响因子：
6.1
通讯作者：
Guangming Li;Mingjian Cao;K. Qin;P. Hollings;N. Evans;E. Seitmuratova
中科院分区：
文献类型：
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作者：
Guangming Li;Mingjian Cao;K. Qin;P. Hollings;N. Evans;E. Seitmuratova
成矿斑岩和斑岩铜矿中的无矿花岗岩在许多方面存在差异，特别是在埃达克岩亲和性和钙碱性特征方面。本文对哈萨克斯坦中部Kounrad、Borly和Sayak矿床的成矿花岗岩类及邻近地区的成矿前和成矿后花岗岩类进行了锆石U-Pb和辉橄榄岩Re-Os定年、全岩地球化学、全岩Sr-Nd-Pb和锆石O-Hf同位素分析。年代学研究表明，成矿前岩浆活动发生在晚泥盆世-早石炭世（361.3- 339.4Ma），随后发生了大规模的铜矿化（Kounrad为325.0-327.3 Ma，Borly为311.4-315.2 Ma，Sayak为309.5-311.4 Ma），最后，晚石炭世矿后无矿花岗岩类侵位（305.0Ma）。这些岩石的地球化学是一致的钙碱性弧岩浆活动的特点是强烈的亏损Nb，Ta和Ti和富集轻稀土元素和大离子亲石元素，建议超俯冲带设置。而Kounrad和Sayak的成矿岩石则表现为高Sr埃达克质特征（517.5-785.3 ppm），Sr/Y（50.60-79.26），（La/Yb）N（9.37-19.62）但Y值较低（6.94- 11.54ppm）和Yb（0.57- 1.07ppm），而Borly成矿岩和Borly西北部和Sayak的贫岩具有正常弧岩浆地球化学特征。Sr-Nd-Hf-O同位素组成显示出三种不同的特征：（1）沙亚克花岗岩类具有非常年轻的下地壳成分（87Sr/86Sr）i= 0.70384 ~ 0.70451，Nd（t）= + 4.9 ~+ 6.0，TDM2（Nd）= 580 ~ 670Ma，Hf（t）= + 11.3 ~+ 15.5; TDMC（Hf）= 330 ~ 600 Ma，δ 18 O = 6.0 ~ 8.1‰），可能是由亏损的幔源岩浆，并在岩浆源区加入5-15%的沉积熔体形成的;（2）沙雅西北部Kt-1花岗岩具有极其富集的Sr-Nd同位素组成（87 Sr/86 Sr）i= 0.71050，Nd（t）=-7.8，TDM2（Nd）= 1700 Ma），可能来源于古陆壳的部分熔融;（3）其它花岗岩类的Sr-Nd成分介于Sayak和Kt-1样品之间，表明是一个年轻的下地壳源，并增加了10-30%的古地壳物质。成矿前的岩浆活动可能与准噶尔-喀什洋向北俯冲导致的幼年下地壳部分熔融有关，而阿克托盖、昆拉德和萨亚克的成矿埃达克质岩石则是增厚的下地壳部分熔融并随后分层形成的。Borly的成矿岩石和成矿后期的贫花岗岩是由正常厚度的年轻下地壳部分熔融形成的。这一构造背景支持了泥盆纪至晚石炭世的安第斯型岩浆弧的存在，这是准噶尔-喀什洋板块俯冲的结果。全岩地球化学与成矿规模之间的联系表明埃达克质岩的成矿潜力高于正常弧岩浆作用。
Ore-forming porphyries and barren granitoids from porphyry Cu deposits differ in many ways, particularly with respect to their adakitic affinity and calc-alkaline characteristics. In this study, zircon U–Pb and molybdenite Re–Os dating, whole rock geochemistry, whole rock Sr–Nd–Pb and zircon O–Hf isotopic analyses were carried out on the ore-forming granitoids from the Kounrad, Borly and Sayak deposits, and also on pre-ore and post-ore granitoids in adjacent regions of Central Kazakhstan. Geochronology results indicate that pre-ore magmatism occurred in the Late Devonian to Early Carboniferous (361.3–339.4 Ma), followed by large scale Cu mineralization (325.0–327.3 Ma at Kounrad, 311.4–315.2 Ma at Borly and 309.5–311.4 Ma at Sayak), and finally, emplacement of the Late Carboniferous post-ore barren granitoids (305.0 Ma). The geochemistry of these rocks is consistent with calc-alkaline arc magmatism characterized by strong depletions in Nb, Ta and Ti and enrichments in light rare earth elements and large ion lithophile elements, suggesting a supra-subduction zone setting. However, the ore-forming rocks at Kounrad and Sayak show adakitic characteristics with high Sr (517.5–785.3 ppm), Sr/Y (50.60–79.26), (La/Yb)N(9.37–19.62) but low Y (6.94–11.54 ppm) and Yb (0.57–1.07 ppm), whereas ore-forming rocks at Borly and barren rocks from northwest of Borly and Sayak have normal arc magma geochemical features. The Sr–Nd–Hf–O isotopic compositions show three different signatures: (1) Sayak granitoids have very young juvenile lower crust-derived compositions ((87Sr/86Sr)i= 0.70384 to 0.70451, ɛNd(t) = + 4.9 to + 6.0; TDM2(Nd) = 580 to 670 Ma, ɛHf(t) = + 11.3 to + 15.5; TDMC(Hf) = 330 to 600 Ma, δ18O = 6.0 to 8.1‰), and were probably generated from depleted mantle-derived magma with 5–15% sediment melt addition in the magma source; (2) the Kt-1 granite from northwest of Sayak shows extremely enriched Sr–Nd isotopic compositions ((87Sr/86Sr)i= 0.71050, ɛNd(t) = − 7.8, TDM2(Nd) = 1700 Ma), likely derived from partial melting of ancient continental crust; (3) other granitoids have transitional Sr–Nd compositions between the Sayak and Kt-1 samples, indicating a juvenile lower crust source with the addition of 10–30% of ancient crustal material. The pre-ore magmatism was probably related to partial melting of juvenile lower crust due to northward subduction of the Junggar–Balkhash Ocean, whereas the ore-forming adakitic rocks at Aktogai, Kounrad and Sayak formed by partial melting of thickened lower crust which subsequently delaminated. The ore-forming rocks at Borly, and the later post-ore barren granites, formed by partial melting of juvenile lower crust with normal thickness. This tectonic setting supports the existence of an Andean-type magmatic arc in the Devonian to the Late Carboniferous, resulting from the subduction of the Junggar–Balkhash oceanic plate. The link between whole rock geochemistry and scale of mineralization suggests a higher metallogenic potential for adakitic rocks than for normal arc magmatism.