張小軍 田江濤 唐毅
摘? 要:路北銅鎳礦床位于覺羅塔格構(gòu)造帶內(nèi),巖體走向受康古爾深大斷裂控制,礦床規(guī)模達(dá)中型。含礦巖體侵入于下石炭統(tǒng)小熱泉子組,圍巖為安山巖與細(xì)砂巖,主要基性-超基性巖為橄欖巖、橄欖輝石巖、輝石巖、輝長巖等。巖體由中心向兩側(cè)基性程度逐漸降低,產(chǎn)狀平緩,主要賦礦巖相為輝石橄欖巖相,礦體多呈似層狀或透鏡狀。含礦角閃輝長巖中鋯石LA-ICP-MS U-Pb定年為(282.9±2.4) Ma,與東天山地區(qū)黃山東、黃山、香山等典型銅鎳礦床及基性-超基性巖體形成時(shí)代一致,為早二疊紀(jì)。認(rèn)為路北礦床為東天山黃山-鏡兒泉銅鎳成礦帶西延部分,該銅鎳礦帶向西具較大的銅鎳找礦空間,康古爾深大斷裂可能為該區(qū)重要的控巖控礦斷裂。
關(guān)鍵詞:東天山西段;路北銅鎳礦床;鋯石U-Pb年代學(xué);找礦潛力
東天山地區(qū)是新疆重要的銅鎳成礦帶[1]?,F(xiàn)已發(fā)現(xiàn)銅、銅鎳、金、鐵、鉛鋅等金屬礦床,相關(guān)類型礦床多成帶分布。區(qū)內(nèi)巖漿巖發(fā)育,黃山東、黃山西、天宇、黃山、香山和土墩等銅鎳礦床從東至西依次產(chǎn)出(圖1),其中黃山東和黃山礦床規(guī)模達(dá)大型。該區(qū)銅鎳礦床均位于庫姆塔格沙垅以東。近年來對(duì)沙隴以西地區(qū)開展了大量地質(zhì)勘查工作,有學(xué)者認(rèn)為東天山西段具銅鎳礦找礦潛力[2]。2012年第一區(qū)域地質(zhì)大隊(duì)通過對(duì)Cu-Ni-Co異常查證,發(fā)現(xiàn)白鑫灘銅鎳礦床[3],開啟了東天山西段尋找銅鎳礦熱潮。
路北銅鎳礦礦床位于庫姆塔格沙垅以西,是在新疆維吾爾自治區(qū)地質(zhì)調(diào)查院2014年化探Ni-Cu-Cr-Co異常檢查基礎(chǔ)上,進(jìn)一步開展槽探和鉆探工作時(shí)發(fā)現(xiàn)的,目前規(guī)模達(dá)中型。路北銅鎳礦礦床研究程度較低,舍建忠等通過對(duì)路北含銅鎳鎂鐵超鎂鐵巖地球化學(xué)特征分析,對(duì)構(gòu)造意義進(jìn)行了分析[4];楊萬志等對(duì)路北發(fā)現(xiàn)銅鎳礦意義進(jìn)行了探討[5];田江濤等通過研究路北銅鎳礦床礦石礦物特征,建立找礦標(biāo)志,分析了找礦意義[6-7];張小軍等在研究恰特卡爾地區(qū)地物化基礎(chǔ)上,建立找礦模型,通過成礦作用分析,指出下一步找礦方向[8-9]。本文對(duì)路北礦床開展巖相學(xué)、鋯石U-Pb定年,厘定該礦床形成時(shí)代、構(gòu)造背景,為進(jìn)一步探討該區(qū)銅鎳找礦潛力及方向提供新資料。
1? 巖體地質(zhì)概況及巖相學(xué)特征
1.1? 地質(zhì)概況
路北銅鎳礦床產(chǎn)于覺羅塔格裂陷槽-小熱泉子島弧帶-康古爾韌性剪切帶北側(cè)(圖2),基性-超基性巖體侵入。受康古爾深大斷裂控制,走向與區(qū)域構(gòu)造線一致。巖體地表形態(tài)呈近臥倒菱形,負(fù)地形出露,主要巖性為輝長巖、輝石巖、橄欖巖等,地表出露寬50~350 m,長6 000 m,面積約0.33 km2。據(jù)鉆孔成果,巖體總體呈SE向緩傾的板狀體,厚度相對(duì)穩(wěn)定,傾角14°~24°。主要巖性為純橄欖巖、含方輝純橄巖、方輝橄欖巖、含角閃石方輝橄欖巖等,橄欖巖、輝石巖、橄欖蘇長巖和橄欖輝長巖為主要賦礦巖性,圍巖為下石炭統(tǒng)小熱泉子組,巖體直接圍巖為安山巖和細(xì)砂巖。局部由于熱接觸變質(zhì)作用發(fā)育角巖化,形成黑云母角巖、長英質(zhì)角巖及各類角巖化巖石。地表見大量褐鐵礦化、孔雀石化和黃鐵鉀礬化。目前地表已圈定12個(gè)礦體,銅鎳礦體長100~930 m,視厚2~46 m,鎳品位0.21%~1.02%,局部較富,最高7.76%。Cu品位0.2%~0.74%,最高1.61%,礦體形態(tài)呈大肚透鏡狀、透鏡狀(圖2)。鉆探資料表明,深部隱伏礦體與地表礦體相連,礦體多呈似層狀或透鏡狀,較平緩。礦床主要礦石類型為浸染狀礦石,局部見塊狀礦石,礦石礦物主要為鎳黃鐵礦、黃銅礦、黃鐵礦、磁黃鐵礦、紫硫鎳礦等,有少量磁鐵礦,方黃銅礦、針鎳礦等。
1.2? 巖相學(xué)特征
路北基性-超基性巖石類型簡單,主要含礦巖相為橄欖巖相、輝石巖相、輝長巖相和橄欖蘇長巖相。
橄欖巖相? 分布于巖體南部地表,出露面積大,主要含礦巖性為橄欖巖,深灰綠色,殘余粒狀結(jié)構(gòu),塊狀構(gòu)造。巖石主要由橄欖石(69%)、輝石(30%)及少量金屬礦物(1%)組成。橄欖石已蝕變,呈孤島狀分布于滑石中,橄欖石間分布有輝石,輝石被滑石、少量透閃石、黑云母交代,呈殘晶狀分布于蝕變礦物中。輝石多為斜方輝石,蝕變礦物約占原礦物的30%,滑石呈鱗片集合體狀交代橄欖石、輝石(圖3-a)。
輝石巖相? 呈透鏡體狀侵入于輝長巖中,主要含礦巖性為輝石巖,深灰色,變余粒狀結(jié)構(gòu),塊狀構(gòu)造。巖石由輝石(84%)和橄欖石(15%)組成,沿解理及邊部已蝕變,主要為透閃石化,晶粒界線不清晰。輝石為斜方輝石,輝石解理中分布有少量角閃石,角閃石不規(guī)則(圖3-b)。
橄欖蘇長巖相? 呈隱伏巖相,僅鉆孔中可見,多分布于輝長巖邊部。主要巖性為橄欖蘇長巖,為礦區(qū)重要含礦巖性,黑色,自形-他形粒狀結(jié)構(gòu),塊狀構(gòu)造。巖石為橄欖石、斜長石和斜方輝石,次為黑云母和角閃石(圖3-c),巖石中次生蝕變作用較明顯,主要為蛇紋石化。
輝長巖相? 發(fā)育于礦區(qū)北部,局部位于閃長巖底部,侵入于石英閃長巖體中,主要含礦巖性為橄欖輝長巖。橄欖輝長巖呈黑色,自形-他形粒狀結(jié)構(gòu),代環(huán)邊結(jié)構(gòu),塊狀構(gòu)造。主要由橄欖石、普通輝石、斜長石及黑云母構(gòu)成(圖3-d),含少量斜方輝石。蝕變作用較強(qiáng),大多蛇紋石化,少量滑石化及鉻綠泥石化,通常位于巖體底部。
2? 樣品采集及測試方法
為保障分析樣品盡量新鮮,用于鋯石U-Pb年齡樣品采自探槽中的角閃輝長巖。鋯石制靶由河北省區(qū)域地質(zhì)礦產(chǎn)調(diào)查研究所完成,陰極發(fā)光顯微照相由北京鋯年領(lǐng)航科技有限公司完成,鋯石U-Pb同位素測試由中國科學(xué)院廣州地球化學(xué)研究所實(shí)驗(yàn)室完成,采用激光剝蝕電感耦合等離子質(zhì)譜儀(LA-ICP-MS)分析,使用標(biāo)準(zhǔn)鋯石91500為外標(biāo)加以校正,每測6個(gè)數(shù)值后進(jìn)行一次91500標(biāo)樣測定,激光光束束斑直徑為30 μm,使用29Si為內(nèi)標(biāo)測定鋯石的U,Th,Pb含量。相關(guān)數(shù)據(jù)采用GLITTER和 Isoplot 軟件進(jìn)行數(shù)據(jù)處理。鋯石原位復(fù)位Hf同位素測試由中國地質(zhì)調(diào)查局西安地質(zhì)調(diào)查中心國土資源部巖漿作用成礦與找礦重點(diǎn)實(shí)驗(yàn)室完成,使用Neptune型多接收等離子體質(zhì)譜儀和Geolas Pro型激光剝蝕系統(tǒng)聯(lián)用方法完成。測試豎斑直徑為44 μm。測試位置與測年點(diǎn)位相同或靠近。每分析10個(gè)樣品測點(diǎn)插入一次標(biāo)樣測定(鋯石標(biāo)準(zhǔn)GJ-1,GJ-1的測試精準(zhǔn)度為0.282 030±40(2SE))。
3? 分析結(jié)果
3.1? Cu,Ni分析元素
Cu,Ni元素含量為新疆維吾爾自治區(qū)礦產(chǎn)實(shí)驗(yàn)測試中心分析數(shù)據(jù),為增加對(duì)比度,筆者選取低品位礦石與高品位礦石進(jìn)行對(duì)比。選取ZK0004(低品位)和ZK1501(高品位)鉆孔中Cu,Ni元素含量為研究對(duì)象。ZK0004中Ni,Cu具相似變化趨勢,Cu,Ni大致呈正相關(guān)關(guān)系,除在一個(gè)異常富集一段,Cu,Ni含量相對(duì)較穩(wěn)定(圖4)。ZK1501中Ni含量隨深度逐漸變大。路北Ni/Cu均值為1.76,黃山東、黃山、香山和白鑫灘礦床Ni/Cu均值分別為2.20、1.90、1.71和1.11[10],路北礦床礦石Ni/Cu比值較東天山其它典型礦床居中。
3.2? 鋯石U-Pb年齡
項(xiàng)目組對(duì)采集的角閃輝長巖樣品進(jìn)行同位素測年,樣品采自礦區(qū)北部的輝長巖相帶。巖石局部具銅鎳礦化,測得巖體LA-ICP-MS的鋯石206Pb/238U-207Pb/235U諧和年齡為(281.4±2.5) Ma,206Pb/238U加權(quán)平均年齡為(282.9±2.4) Ma(圖5,表1)。表明該套雜巖和相關(guān)銅鎳硫化物礦床形成于早二疊世早期,與東天山地區(qū)黃山東(274±3) Ma、黃山(269±2) Ma、香山(285±1.2) Ma等典型銅鎳礦床及基性-超基性巖體形成時(shí)代一致[11-15]。
4? 討論
本次獲得的路北銅鎳礦床角閃輝長巖成巖年齡為(282.92.4) Ma,稍晚于礦區(qū)北部角閃輝長巖(287.9±1.6) Ma[16],略早于最晚期侵位的石英閃長巖[17],屬早二疊世后碰撞伸展環(huán)境下幔源巖漿上涌產(chǎn)物。路北銅鎳礦床礦石Ni,Cu成礦元素及巖相變化特征表明,路北巖體深部具較好找礦前景。近年來,覺羅塔格構(gòu)造帶西段發(fā)現(xiàn)路北、白鑫灘銅鎳礦,成礦規(guī)模已達(dá)中型,成巖時(shí)代與東天山地區(qū)發(fā)現(xiàn)的黃山、黃山東、葫蘆等典型銅鎳礦床形成時(shí)代一致(表2),該帶為黃山-鏡兒泉銅鎳礦帶西延部分。
5? 結(jié)論
路北銅鎳礦中輝長巖成巖年齡為(282.9±2.4) Ma (MSWD=1.3,n=28),與東天山地區(qū)發(fā)現(xiàn)的黃山、黃山東、葫蘆等典型銅鎳礦床形成時(shí)代一致。路北銅鎳礦的發(fā)現(xiàn),表明覺羅塔格西段地區(qū)具尋找銅鎳礦巨大潛力,大大拓寬了東天山銅鎳找礦空間。
致謝:李平高級(jí)工程師對(duì)本文的幫助指導(dǎo),匿名審稿專家的認(rèn)真審閱,給予寶貴的修改意見,在此一并致以忠心感謝!
參考文獻(xiàn)
[1]? ? 毛景文,F(xiàn)ranco PIRAJNO,張作衡,等.天山-阿爾泰東部地區(qū)海西晚期后碰撞銅鎳硫化物礦床:主要特點(diǎn)及可能與地幔柱的關(guān)系[J].地質(zhì)學(xué)報(bào),2006(7):925-942.
[2]? ? 鐘清,孟小紅,姚敬金,等.地物化綜合信息在東天山西段的找礦預(yù)測結(jié)果[J].物探與化探,2006,30(1):21-25.
[3]? ? 李鑫,王敦科,趙樹銘.哈密白鑫灘巖漿型銅鎳硫化物礦床的發(fā)現(xiàn)[J].新疆地質(zhì),2014,32(4):466-469.
[4]? ? 舍建忠,楊萬志,馮長麗,等.路北含銅鎳鎂鐵超鎂鐵巖地球化學(xué)特征及其構(gòu)造意義[J]. 新疆地質(zhì),2016,1(1):29-41.
[5]? ? 楊萬志,任燕,田江濤,等.東天山路北銅鎳礦的發(fā)現(xiàn)及意義[J].礦物巖石地球化學(xué)通報(bào),2017,36(1):112-120 .
[6]? ? 田江濤,李大海,王成,等.東天山西段路北銅鎳礦床地質(zhì)特征及找礦標(biāo)志[J].西部探礦工程,2017,29 (4):88-191.
[7]? ? 田江濤,李大海,張小軍,等.東天山恰特卡爾-海豹灘銅鎳礦帶特征及資源潛力[J].新疆地質(zhì),2018,36(3):315-322.
[8]? ? 張小軍,田江濤,李大海,等.新疆鄯善縣恰特卡爾地區(qū)基性-超基性巖型銅鎳找礦模型及礦產(chǎn)預(yù)測[J].新疆地質(zhì),2018,36(3):323-329.
[9]? ? 張小軍,田江濤,唐毅,等.新疆鄯善縣路北銅鎳礦成礦作用分析及找礦方向[J].新疆地質(zhì),2020,38(3):365-371.
[10]? 王亞磊,張照偉,尤敏鑫,等.東天山白鑫灘銅鎳礦鋯石U-Pb年代學(xué)、地球化學(xué)特征及對(duì)Ni-Cu找礦的啟示[J].中國地質(zhì),2015,42(3):452-467.
[11]? 三金柱,秦克章,湯中立,等.東天山圖拉爾根大型銅鎳礦區(qū)兩個(gè)鎂鐵-超鎂鐵巖體的鋯石U-Pb定年及其地質(zhì)意義[J].巖石學(xué)報(bào),2010,26(11):3027-3035.
[12]? 馮宏業(yè),許英霞,秦克章,等.東天山圪塔山口鎂鐵-超鎂鐵質(zhì)巖體地球化學(xué)、鋯石U-Pb年代學(xué)及其對(duì)Ni-Cu成礦的指示[J].巖石學(xué)報(bào),2014, 30(6):1558-1574.
[13]? 韓寶福,宋彪,陳立輝,等.新疆喀拉通克和黃山東含銅鎳礦鎂鐵-超鎂鐵雜巖體的 SHRIMP 鋯石 U-Pb 年齡及其地質(zhì)意義[J].科學(xué)通報(bào),2004, 49(22):2324-2328.
[14]? Qin K Z, Su B X, Patrick A S, et al. SIMS Zircon U- Pbgeocheronology and Sr-Nd isotopes of Ni-Cu beraing mafic-ultramafic intrusion in eastern Tianshan and Beishan incorrelation with flood basalts in Tarim basin(NW China):Conetraints on a CA 280 Ma mantle plume[J].American Journalof Science,2011,311: 1-23.
[15]? 秦克章,方同輝,王書來,等.東天山板塊構(gòu)造分區(qū)、演化與成礦地質(zhì)背景研究[J].新疆地質(zhì),2002,20:302 -307.
[16]? Chen Bao-Yun, Yu Jin-Jie, Liu Shuai-Jie. Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion. Lithos,2018,308-309,329-345.
[17]? Li Ping, Zhao Tongyang, Zhu Zhixin,et ai. First Report of Zircon U-Pb Ages from Lubei Cu-Ni Sulfide Deposit in East Tianshan of Central Asian Orogenic Belt (NW China). Acta Geologica Sinica (English Edition),2018, 92(2): 855-856.
[18]? Chen Jiping, Liao Qunan, Zhang Xionghua, et ai. Contrast of Huangshandong and Xiangshan Mafic-Ultramafic Complex, East Tianshan. Earth Science -Journal of China University of Geosciences,2013,38(6): 1183-1196.
[19]? Zhao Yun, Xue Chunji, Zhao Xiaobo,et al. Magmatic Cu-Ni sulfide mineralization of the Huangshannan mafic-untramafic intrusion, Eastern Tianshan, China. Journal of Asian Earth Sciences,2015,105: 155-172.
[20]? Mao YaJing, Qin KeZhang,Tang DongMei,et al.Crustal contamination and sulfide immiscibility history of the Permian Huangshannan magmatic Ni-Cu sulfide deposit, East Tianshan, NW China. Journal of Asian Earth Sciences,2016,129: 22-37.
[21]? Zhou Meifu, Lesher C. Michael, et al.Geochemistry and petrogenesis of 270 Ma Ni-Cu-(PGE) sulfide-bearing mafic intrusions in the Huangshan district, Eastern Xinjiang, Northwest China: implications for the tectonic evolution of the Central Asian orogenic belt. Chemical Geology,2004,209: 233-257.
[22]? Li Yuechen, Zhao Guochun, Qu Wenjun,et al. Re Os isotopic dating of the Xiangshan deposit, East Tianshan, NW China. Acta Petrologica Sinica,2006, 22(1):245 -251.
[23]? Han Chunming, Xiao Wenjiao, Zhao Guochun, et al.In-situ U-Pb, Hf and Re-Os isotopic analyses of the Xiangshan Ni-Cu-Co deposit in Eastern Tianshan (Xinjiang), Central Asia Orogenic Belt: Constraints on the timing and genesis of the mineralization. Lithos,2010,120: 547-562.
[24]? Xiao Qinghua, Qin Kezhang, Tang Dongmei, et al.Xiangshanxi composite Cu-Ni-Ti-Fe deposit belongs to comagmatic evolution product; Evidences from ore microscopy, zircon U-Pb chronology and petrological geochemistry, Hami, Xinjiang, NW China Acta Petrologica Sinica. 2010,26(2) :503-522.
[25]? Li Dedong, Wang Yuwang, Wang Jingbin,et al.The timing order of mineralization and diagenesis for Xiangshan complex rocks,Xinjiang.Acta Petrologica Sinica,2012,28(7) :2103-2112.
[26]? Sun Tao, Qian Zhuangzhi, Tang Zhongli, et al.Zircon U-Pb chronology, platinum group element geochemistry characteristics of Hulu Cu-Ni deposit, East Xinjiang, and its geological significance. Acta Petrologica Sinica,2010,26(11):3339 -3349.
[27]? Chen Shiping, Wang Denghong, Qu Wenjun, et al.Geological features and ore formation of the Hulu Cu-Ni sulfide deposit, earstern Tianshan, Xinjiang. Xinjiang Geology,2005,23(3): 230-233.
[28]? Sun Tao, Qian Zhuangzhi, Li Chusi,et al. Petrogenesis and economic potential of the Erhongwa mafic-ultramafic intrusion in the Central Asian Orogenic Belt, NWChina: Constraints from olivine chemistry, U-Pb age and Hf isotopes of zircons, and whole-rock Sr-Nd-Pb isotopes. Lithos,2013,182-183:185-199.
[29]? WANG Yalei,ZHANG Zhaowei,YIN Xiwen,et al.Chronological and Geochemical Characteristics of Sangong Cu-Ni Mineralization Intrusion in Eastern Tianshan of Xinjiang and Their Implications for Cu-Ni Mineralization. Acta Geoscientica Sinica,2016,37(6): 699-710.
[30]? San Jinzhu, Qin Kezhang, Tang Zhongli, et al.Precise zircon U-Pb age dating of two mafic-ultramafic complexes at Tulargen large Cu-Ni district and its geological implications. Acta Petrologica Sinica,2010,26(10): 3027-3035.
[31]? Wang Yalei,Zhang Zhaowei,You Minxin,et al.Chronological and gechemical charcateristics of the Baixintan Ni-Cu deposit in Eastern Tianshan Mountains, Xinjiang, and their implications for Ni-? ? Cu mineralization. Geology in China,2015,42(3):452-467.
[32]? Feng Yanqing, Qian Zhuangzhi, Duan Jun,et al.Genesis and Ore forming Potential of Mafic-Ultramafic Intrusions in the Western Part of East Tianshan Cu-Ni Metallogenic Belt, Xinjiang. Acta Geologica Sinica,2017,91(4): 792-811.
[33]? Zhao B B, Deng Y F, Zhou T F,et al.Petrogenesis of the Baixintan Ni-Cu sulfide-bearing mafic-ultramafic intrusion, East Tianshan: Evidence from geochronology, petrogeochemistry and Sr-Nd isotope. Acta Petrologica Sinica. 2018,34(9):2733-2753.
[34]? Feng Yanqing, Qian Zhuangzhi, Duan Jun, et al. Geochronological and geochemical study of the Baixintan magmatic Ni-Cu sulphide deposit: New implications for the exploration potential in the western part of the East Tianshan nickel belt (NW China). Ore Geology Reviews,2018,95:366-381
[35]? Mi Baoxin, Li Ping, Jin Liuyuan, et al.Geochemical Characteristics and Metallogenic Potential of the Mafic ultramafic Rocks Form Longxi in the Eastern Tianshan Mountains. Xinjiang Geology,2019,37(4): 498-504.
[36]? Ren Minghao, Wang Yan, Ni Kang, et al.Differentiation of magmas in the formation of Permian mafic-ultramafic intrusions in the Dacaotan area Eastern Tianshan: Implications for Ni Cu-PGE sulfide mineralization potentials. Acta Petrologica Sinica,2013,29(10): 3473-3486.
[37]? Sun Yan, Wang Jingbin, Lv Xiaoqiang, et al.Geochronology, petro genesis and tectonic implications of the newly discovered Cu-Ni? ?sulfide-mineralized Yueyawan gabbroic complex,Kalatag district, northwestern Eastern Tianshan, NW China.Ore Geology Re? ? ? ? ? ? ? ? ? ? views, 2019,109: 598-614.