張照偉，錢兵，王亞磊，李世金，劉長征

(1.國土資源部巖漿作用成礦與找礦重點(diǎn)實(shí)驗(yàn)室，西安地質(zhì)礦產(chǎn)研究所，陜西 西安　710054；2.青海省地質(zhì)調(diào)查局，青海 西寧　810001；3.青海省第五地質(zhì)礦產(chǎn)勘查院，青海 西寧　810028)

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青海省夏日哈木銅鎳礦床巖石地球化學(xué)特征及其意義

張照偉1，錢兵1，王亞磊1，李世金2，劉長征3

(1.國土資源部巖漿作用成礦與找礦重點(diǎn)實(shí)驗(yàn)室，西安地質(zhì)礦產(chǎn)研究所，陜西 西安710054；2.青海省地質(zhì)調(diào)查局，青海 西寧810001；3.青海省第五地質(zhì)礦產(chǎn)勘查院，青海 西寧810028)

摘要：新發(fā)現(xiàn)的青海省夏日哈木超大型鎳礦床，在國內(nèi)是僅次于金川巖漿銅鎳礦床的第二大礦床。礦區(qū)發(fā)育5個(gè)鎂鐵-超鎂鐵巖體，目前僅Ⅰ號鎂鐵-超鎂鐵巖體內(nèi)發(fā)現(xiàn)了具有經(jīng)濟(jì)價(jià)值的超大型礦體，其他4個(gè)巖體多為鎂質(zhì)橄欖巖及榴輝巖，是多種構(gòu)造體制疊加巖漿活動的結(jié)果。分析發(fā)現(xiàn)Ⅰ號巖體所有巖石的SiO2含量為34.11%～54.28%，其m/f值為2.01～4.93，屬鐵質(zhì)系列的鎂鐵-超鎂鐵巖石。通過對橄欖石Fo值與Ni含量研究表明，存在多期次的巖漿成礦作用，橄欖石Fo值與Ni含量正相關(guān)和負(fù)相關(guān)的協(xié)變關(guān)系，說明存在早期硫化物不混溶作用。結(jié)合區(qū)域年代學(xué)綜合分析認(rèn)為，夏日哈木超大型巖漿銅鎳硫化物礦床的形成，是早泥盆世早期巖漿活動于柴達(dá)木盆地邊緣東昆侖造山帶夏日哈木地區(qū)具體的成礦表現(xiàn)。在其Ⅰ號和Ⅱ號巖體的深部，仍具有較大的找礦潛力，而其他3個(gè)鎂鐵-超鎂鐵質(zhì)多以鎂質(zhì)橄欖巖為主，不具備鎳礦成礦條件，可能沒有發(fā)現(xiàn)銅鎳礦的經(jīng)濟(jì)價(jià)值。

關(guān)鍵詞：巖石地球化學(xué)特點(diǎn)，鎂鐵-超鎂鐵質(zhì)巖體，銅鎳礦床，找礦方向，夏日哈木，青海省

青海省夏日哈木巖漿銅鎳硫化物礦床是近兩年在東昆侖造山帶發(fā)現(xiàn)的超大型礦床(李世金等，2012)，在國內(nèi)是僅次于甘肅省金川巖漿銅鎳(鉑族)硫化物礦床的第二大鎳礦床，也是繼1996年加拿大沃爾斯貝(Voisey’s Bay)巖漿硫化物礦床發(fā)現(xiàn)以來近20年全球鎳礦最重要的發(fā)現(xiàn)(LI et al., 2015)。夏日哈木地區(qū)發(fā)育5個(gè)鎂鐵-超鎂鐵巖體，110萬t的鎳金屬量只賦存于其中的一個(gè)鎂鐵-超鎂鐵質(zhì)巖體內(nèi)，其余4個(gè)巖體的含礦性尚不清楚，這5個(gè)鎂鐵-超鎂鐵質(zhì)侵入巖體之間的關(guān)系，無疑直接影響到進(jìn)一步的含礦性評價(jià)和勘探找礦方向。通過詳細(xì)的野外調(diào)查和鉆孔巖心編錄，發(fā)現(xiàn)夏日哈木巖漿銅鎳硫化物礦床的含礦巖體是由橄欖巖、輝石巖及少量輝長巖組成，是多期次巖漿活動的結(jié)果。鎳礦體的形成只與橄欖巖及輝石巖有關(guān)，輝長巖在含礦的超鎂鐵質(zhì)巖之前之后均有發(fā)育。可見，夏日哈木巖漿銅鎳硫化物礦床及其含礦巖體的地質(zhì)特征有待進(jìn)一步鑒別，其硫化物熔離機(jī)制與成礦過程、巖漿源區(qū)性質(zhì)及構(gòu)造背景也是制約深部找礦及含礦巖體形成過程的關(guān)鍵因素。本研究擬從夏日哈木鎂鐵-超鎂鐵質(zhì)巖體的空間形態(tài)和巖相分異入手，結(jié)合巖體的巖石地球化學(xué)特點(diǎn)和含礦巖體的橄欖石成分，進(jìn)一步探討夏日哈木區(qū)域內(nèi)鎂鐵-超鎂鐵質(zhì)巖體的勘探找礦方向，初步總結(jié)可能產(chǎn)出的構(gòu)造地質(zhì)背景和成礦環(huán)境，對于深化巖漿銅鎳硫化物礦床的形成機(jī)理認(rèn)識、指導(dǎo)區(qū)域內(nèi)類似巖體及礦床的發(fā)現(xiàn)與勘查，具有重要意義。

1區(qū)域地質(zhì)構(gòu)造背景

青海省夏日哈木鎂鐵-超鎂鐵質(zhì)侵入巖體及巖漿銅鎳硫化物礦床位于柴達(dá)木地塊南緣東昆侖造山帶中(圖1a)。東昆侖造山帶以昆中區(qū)域性大斷裂為界又可進(jìn)一步分為昆北和昆南造山帶。昆北造山帶中發(fā)育有大量的391～410 Ma的花崗巖，這些花崗巖侵入到前寒武紀(jì)變質(zhì)基底及古生代火山沉積地層中，零星可見三疊紀(jì)沉積地層(圖1b)。在昆北造山帶的東部，發(fā)現(xiàn)有～428 Ma的榴輝巖(MENG et al., 2013)。其他幾處蛇綠混雜巖的年齡變化在467～518 Ma，并且這些蛇綠混雜巖的玄武質(zhì)巖石表現(xiàn)出了典型的MORB 特征(BIAN et al., 2004；宋謝炎等，2009；楊合群等，2010；MENG et al., 2013；校培喜等，2014)。祁漫塔格早古生代巖漿弧以昆北斷裂帶為界與柴達(dá)木盆地接壤，昆南增生楔雜巖帶則以昆南斷裂帶為界與巴顏喀拉造山帶毗鄰。青海省夏日哈木超大型巖漿銅鎳硫化物礦床產(chǎn)出于祁漫塔格早古生代巖漿弧內(nèi)，臨近黑山-那陵格勒斷裂(圖1c)。礦區(qū)出露地層主要為古元古代白沙河巖群，巖石類型為黑云斜長片麻巖、眼球狀混合片麻巖、大理巖、二云石英片巖等，原巖恢復(fù)為碎屑巖-碳酸鹽巖-火山巖建造，經(jīng)歷了角閃巖相區(qū)域變質(zhì)作用(張雪亭等，2007；耿林等，2007；李榮社等，2008；范麗琨等，2009；校培喜等，2014)。幾個(gè)不同時(shí)代不同規(guī)模的巖漿銅鎳硫化物礦床發(fā)育于柴達(dá)木地塊的北緣及其附近，如牛鼻子梁(柴達(dá)木西北緣402 Ma)(錢兵等，2015)、亞曲(東南祁連441 Ma)、裕龍溝(東南祁連443 Ma)(ZHANG et al., 2014)。但牛鼻子梁、亞曲及裕龍溝等由于巖體規(guī)模較小至今尚未發(fā)現(xiàn)具有較大經(jīng)濟(jì)價(jià)值的礦體。

圖1　青海省夏日哈木銅鎳礦區(qū)域構(gòu)造及地質(zhì)略圖(LI et al., 2015)Fig.1　The schematic tectonic and geological map of Xiarihamu in Qinghai Province

2夏日哈木巖(礦)體地質(zhì)特點(diǎn)

夏日哈木巖漿銅鎳硫化物礦床所在區(qū)域目前已發(fā)現(xiàn)5個(gè)鎂鐵-超鎂鐵質(zhì)巖體，對應(yīng)的巖體編號分別為Ⅰ號、Ⅱ號、Ⅲ號、Ⅳ號和Ⅴ號(圖2)。夏日哈木銅鎳礦體基本都產(chǎn)在Ⅰ號巖體內(nèi)，筆者所研究及討論的也主要是Ⅰ號巖體(圖3)。礦區(qū)北部的正長花崗巖基形成于(391.1±1.4) Ma(王冠等，2013)。斷裂構(gòu)造以近東西向和北西西向?yàn)橹鳎纬蓵r(shí)代早。北東向和南北向斷裂規(guī)模相對較小，形成時(shí)代晚，經(jīng)常錯(cuò)斷近東西向和北西西向斷層(圖2)。Ⅱ號巖體地表露頭主要是輝石巖，發(fā)現(xiàn)少量硫化物，在其旁邊發(fā)育榴輝巖。Ⅲ號巖體主要是鎂質(zhì)橄欖巖，同樣發(fā)現(xiàn)有榴輝巖和榴閃巖。Ⅳ號和Ⅴ號巖體基本都是鎂質(zhì)橄欖巖。

夏日哈木礦區(qū)Ⅰ號巖體長約1.5 km，寬約0.8 km，長軸方向近東西向，西段略向南偏轉(zhuǎn)。將所有施工鉆孔投影到平面圖上，主要是12號勘探線以西，以0.5%的Ni品位劃分為見礦鉆孔及未見礦鉆孔，從而初步確定了礦體及巖體的邊界(圖3a)。巖體頂界面東高西低，東段出露于地表，西段隱伏于地下，且越向西埋深越深(圖3b、圖3e)，總體形態(tài)為向西傾伏的巖床(圖3)。夏日哈木礦區(qū)Ⅰ號巖體在地表有氧化蝕變帶及鐵帽出露(圖4b)，主要集中在0號勘探線東西兩側(cè)，1號勘探線與4號勘探線之間的區(qū)域(圖3a)。從3條勘探線(2號、9號和17號勘探線)鉆孔縱剖面圖(圖3c、圖3d、圖3e)來看，巖體巖性主要是輝石巖、橄欖巖、輝長巖，含少量的花崗巖脈(圖4a)，并且橄欖巖相越向西橄欖石含量逐漸增多，同時(shí)埋深加大，圍巖地層厚度增厚。在鉆孔橫剖面圖上，上述情況則更加明顯直觀(圖3f、圖3g、圖3h)，沿著NM線248°方向，巖石基性程度變高，巖體埋深增大，橄欖石含量增多，礦體增厚變富，并且向南向北邊部巖體和礦體變薄甚至尖滅(圖3f)。

圖2　青海省夏日哈木巖漿銅鎳硫化物礦區(qū)巖體地質(zhì)分布略圖(據(jù)張照偉等，2015b)Fig.2　Schematic geological map for mafic-ultramafic intrusions from Xiarihamu magmatic Ni-Cu deposit inQinghai Province (After ZHANG et al., 2015b)

夏日哈木礦區(qū)鎳礦體主要賦存于輝石巖與橄欖巖中，且以二輝巖和二輝橄欖巖為主，不含礦的輝長巖與含礦的輝石巖及橄欖巖明顯不是同期的產(chǎn)物。鎳礦體主要賦存于夏日哈木礦區(qū)Ⅰ號巖體2號(AB線)勘探線以西地表以下的區(qū)域，在9號勘探線、11號勘探線的位置區(qū)域，鎳礦體達(dá)到了最厚(超過300 m)，隨著勘探線號的變大(向西)，巖體變薄，埋深增厚，橄欖石增多，鎳礦體變富(圖3c、圖3d、圖3e)。礦石礦物主要為鎳黃鐵礦、磁黃鐵礦及少量的黃銅礦(圖4f、圖4g)，可見明顯的橄欖石被輝石包裹的典型包橄結(jié)構(gòu)(圖4d、圖4e)。

3巖石地球化學(xué)特點(diǎn)

3.1巖石地球化學(xué)特征

Ⅰ號巖體中各種巖石的主量元素分析數(shù)據(jù)見表1。所有巖石的SiO2含量為34.11%～54.28%，均屬基性-超基性巖石。m/f值為2.01～4.93，屬鐵質(zhì)系列。

圖3　(a)青海省夏日哈木礦區(qū)Ⅰ號巖體縱投影、(b)平面及(c)、(d)、(e)、(f)、(g)、(h)剖面地質(zhì)略圖Fig.3　Schematic geological map for vertical projection (a)、plan (b) and profile (c)、(d)、(e)、(f)、(g)、(h) from Xiarihamu intrusion Ⅰ in Qinghai Province

各種巖石的稀土元素總量均較低，∑REE=7.62×10-6～51.23×10-6。橄欖巖相巖石的稀土元素豐度大多低于輝石巖相的相應(yīng)豐度，而后兩類巖石又低于輝長巖相的豐度。大多數(shù)超鎂鐵質(zhì)巖石沒有明顯的Eu異常，少數(shù)樣品有弱的負(fù)Eu異常。鎂鐵質(zhì)巖石普遍有不同程度的正Eu異常。各種巖石均具有輕稀土元素富集型配分曲線(圖5)。(La/Yb)N=1.74～10.66，平均值為3.69；(La/Sm)N=1.19～3.93，平均值為2.16；(Gd/Yb)N=1.03～2.41，平均值為1.57。顯示了輕-重稀土元素之間、輕稀土元素之間分餾強(qiáng)，而重稀土元素之間分餾弱的特征。原始地幔標(biāo)準(zhǔn)化的微量元素配分曲線見圖5。各種巖石具有相似的微量元素配分曲線，顯著的Ba、Nb負(fù)異常。

3.2橄欖石成分特征

對鉆孔巖心ZK602S和ZK1507系統(tǒng)采集樣品進(jìn)行礦物晶體化學(xué)成分分析，選擇貧硫化物和無硫化物的二輝橄欖巖與二輝巖進(jìn)行橄欖石Fo值與Ni含量的系統(tǒng)對比。從橄欖石Fo值與橄欖石Ni含量的協(xié)變圖(圖6)可以看出，隨著鉆孔深度的增加，橄欖石Fo值與Ni含量表現(xiàn)出了兩種截然不同的相關(guān)關(guān)系，既有正相關(guān)也有負(fù)相關(guān)，一是說明巖漿演化的早期既有硫化物不混溶作用發(fā)生，從巖石學(xué)及顯微照片也證實(shí)了這一點(diǎn)(圖4c)，橄欖石晶體包裹了硫化物包體，而后又被較大的斜方輝石晶體所包裹。另一方面，說明成礦過程并非一次巖漿作用的結(jié)果，是多期次巖漿活動的產(chǎn)物。

Cp. 黃銅礦；Pl. 斜長石；Po. 磁黃鐵礦；Pn. 鎳黃鐵礦；Ol. 橄欖石；Cpx. 單斜輝石；Opx. 斜方輝石;a.鉆孔巖芯團(tuán)塊 　 　狀礦石；b.地表露頭輝石巖；c.橄欖石中的硫化物包體；d.含長二輝巖顯微照片；e.包橄結(jié)構(gòu)；f.黃銅礦、磁黃鐵礦及鎳黃鐵礦共生；g.磁黃鐵礦與黃銅礦共生圖4　夏日哈木礦區(qū)巖礦石及顯微照片F(xiàn)ig.4　Microphotographs of rocks and ore minerals in Xiarihamu magmatic Ni-Cu sulfide deposit

樣品編號XH-8XH-10XH-58XH-91XH-2XH-13XH-15XH-24XH-28XH-56XH-83XH-b85巖性輝長巖輝石巖橄 欖 輝 石 巖SiO254.2847.2649.3647.7337.737.2738.1639.7739.1441.7139.6438.53Al2O319.413.762.673.672.291.402.254.621.541.673.332.33CaO7.118.641.144.582.151.521.802.260.821.271.901.27Fe2O31.911.902.921.643.185.234.381.924.652.713.294.84FeO5.0112.659.4212.0312.395.096.328.764.96.976.475.72K2O2.290.060.220.150.050.150.080.350.390.050.190.14MgO2.5220.7829.5423.5831.9537.0635.6632.5437.1236.3536.4235.03MnO0.120.170.140.150.130.130.130.120.110.100.140.11Na2O3.570.350.270.360.120.090.200.310.070.080.400.16P2O50.180.020.030.020.010.010.020.010.020.020.040.01TiO21.080.280.160.240.120.110.120.180.10.170.270.11LOI2.701.972.3747.5211.4510.587.4911.168.457.6610.64Total100.1897.8498.2498.1597.6199.5199.798.33100.0299.599.7598.89

續(xù)表1

樣品編號XH-8XH-10XH-58XH-91XH-2XH-13XH-15XH-24XH-28XH-56XH-83XH-b85巖性輝長巖輝石巖橄 欖 輝 石 巖Mg#0.400.720.810.760.790.870.860.850.880.870.870.86Cr25.22570362129023171713750278338010681141258Co19.90382351394421142218173172212175169Ni43.5777514311756772452918416941993141576334634343Cu17.001818327916411127350577628145793307338Zn74.8074.588.593.810583.681.59490.256.784.577.5Rb117.005.3714.16.951.484.373.3618.223.71.9410.23.37Sr494.0024.426.629.810.118.64756.716.35.5581.132.9Cs6.532.095.384.181.250.60.6112.8120.661.360.91Ba501.0013.938176.0914.416.143.656.311.265.610.7Pb5.6910.513.65.155.798.95.196.011.293.5115.64.04Bi0.053.3611.20.992.991.531.377.011.492.870.934.02Th5.860.241.10.390.170.450.310.50.690.370.810.31U1.140.050.220.080.050.140.070.30.190.090.290.25Nb9.960.230.630.420.320.380.310.4710.371.160.46Ta0.500.050.050.110.050.050.050.060.060.050.070.05Zr202.0015.710.814.68.1710.18.8611.623.512.331.47.79Hf5.580.580.30.420.260.260.270.320.530.380.760.22Sb0.310.050.120.070.090.140.080.20.150.050.070.12Ti6510.001475827125868565467110806039591537677V158.0024678.418481.921.143.543.91752.649.722.6La22.101.132.041.20.611.10.821.441.250.963.460.86Ce46.703.353.762.921.542.571.973.273.032.387.282.1Pr6.030.550.420.410.230.330.280.410.420.360.890.27Nd24.902.911.51.981.121.441.271.811.771.673.71.37Sm6.761.050.420.620.380.40.40.540.530.561.020.35Eu2.030.310.120.210.120.110.160.20.150.140.370.11Gd5.661.110.340.630.420.460.410.650.420.530.940.42Tb0.940.250.060.140.090.070.070.10.070.120.170.07Dy5.511.50.440.890.60.440.530.640.430.81.090.4Ho1.060.330.090.20.120.080.110.140.080.160.220.1Er2.940.850.260.530.340.270.280.40.210.430.580.28Tm0.400.130.050.090.060.050.050.050.050.060.090.05Yb2.830.850.310.60.360.230.270.40.240.440.580.26Lu0.420.130.050.090.060.050.050.060.050.070.090.05Sc17.5041.6016.5030.0016.707.7411.608.865.9013.3010.607.52Y31.809.032.715.583.602.573.064.012.384.636.382.77

續(xù)表1

樣品編號XH-87XH-52XH-41XH-43XH-46XH-48XH-b51XH-54XH-104XH-124XH-128HM-1巖性橄欖輝石巖輝 石 橄 欖 巖SiO241.5442.4241.2336.5137.0035.0038.9337.3937.8234.8434.1136.35Al2O31.217.053.531.810.991.341.911.833.381.571.180.75CaO0.945.672.271.180.511.421.710.871.981.250.231.02Fe2O34.872.832.205.495.673.662.426.633.535.234.814.77FeO6.256.416.937.738.6711.359.905.579.7711.028.426.97K2O0.100.340.810.170.090.100.080.330.150.070.130.13MgO36.429.1932.7535.2535.9336.0335.2634.8533.2034.2836.1236.98MnO0.110.130.140.150.140.140.140.120.140.140.100.13Na2O0.090.800.140.180.070.180.200.100.350.180.050.05P2O50.020.010.030.050.030.020.020.010.050.040.040.02TiO20.100.350.140.270.100.080.120.130.220.080.060.06LOI8.075.088.5510.709.568.437.3111.307.709.3012.9611.07Total99.70100.2898.7299.4998.7697.7598.0099.1398.2998.0098.2198.3Mg#0.860.850.870.830.820.810.840.840.820.800.830.85Cr592.00555.00592.00680.00258.00713.00818.00231.00962.00476.001625.00512.00Co175.0090.70172.00277.00332.00405.00299.00158.00310.00287.00350.00192.00Ni3354.001337.002708.008970.0011067.007308.005167.002094.0011512.009782.0015210.004694.00Cu84.5070.30335.001253.001968.001226.00620.00222.001753.001173.001351.00568.00Zn79.0069.4076.1087.40102.0081.4094.6072.90103.00174.0093.9070.90Rb4.6715.80102.008.824.602.323.0018.907.741.174.438.13Sr10.70166.0019.3024.109.4625.7023.0026.7055.5039.006.3312.40Cs1.473.3089.903.171.530.590.861.561.020.782.256.51Ba18.3028.4024.6029.6012.3022.8038.0055.6029.308.9311.3013.50Pb2.496.062.934.946.277.568.504.5111.00138.003.053.07Bi0.790.301.155.185.021.751.650.345.3911.1017.604.84Th0.441.860.540.760.640.190.290.650.820.200.710.32U0.131.010.140.170.180.050.060.220.150.280.210.06Nb0.511.471.301.120.460.240.300.880.730.170.970.26Ta0.050.150.060.080.050.050.050.090.050.050.060.05Zr10.2023.2015.6031.9015.207.7910.9016.5034.104.7812.003.56Hf0.260.730.380.810.360.230.300.410.770.140.230.10Sb0.070.250.090.130.110.050.050.210.140.490.220.20Ti543.002057.00832.001391.00549.00500.00755.00798.001202.00430.00319.00379.00V30.7082.3035.1042.6019.5024.8049.7015.2040.316.6018.719.80La0.833.001.562.280.930.930.821.892.080.491.400.62Ce1.926.973.515.192.042.091.914.414.601.232.671.40Pr0.250.830.470.710.260.290.280.530.610.150.310.18Nd1.113.742.153.171.151.221.272.382.650.601.140.76Sm0.331.150.630.940.290.370.450.580.730.210.250.23Eu0.100.330.200.260.080.120.160.100.240.070.080.06Gd0.311.240.560.830.280.320.420.500.720.260.240.26Tb0.060.210.110.170.050.070.090.080.140.050.050.05Dy0.371.360.671.000.350.410.560.450.870.250.250.26Ho0.080.280.130.200.070.080.120.090.170.050.050.06Er0.200.850.350.550.210.220.320.270.480.140.160.15Tm0.050.100.060.090.050.050.050.050.070.050.050.05Yb0.230.700.380.560.240.250.360.220.50.150.190.13Lu0.050.090.060.090.050.050.060.050.080.050.050.05Sc9.7018.5010.2011.006.037.9113.206.2010.205.865.938.12Y2.208.583.796.082.102.393.572.845.281.591.711.49

續(xù)表1

樣品編號HM-5HM-8HM-9HM-29HM-33HM-36HM-39HM-69HM-73HM-74HM-77HM-81巖性輝 石 橄 欖 巖SiO240.6438.4836.3338.6438.0138.4536.9540.9837.3936.5437.3836.48Al2O33.022.163.240.881.092.963.763.831.231.020.571.44CaO3.762.382.140.681.271.692.202.190.750.740.821.04Fe2O33.823.562.244.023.484.664.423.524.184.506.085.22FeO5.858.6911.216.327.834.359.456.505.325.606.395.41K2O0.180.150.160.060.200.210.100.170.120.080.050.15MgO34.0234.5533.3938.7638.0936.1832.1134.2138.5138.8137.2037.09MnO0.140.140.120.120.160.110.140.150.120.120.130.13Na2O0.300.310.330.080.160.230.450.490.070.060.050.07P2O50.010.010.010.040.020.010.010.020.010.010.010.01TiO20.240.160.200.100.090.130.140.370.120.080.050.11LOI7.508.519.139.048.1110.858.706.4810.8211.0310.2411.62Total99.4899.1098.598.7498.5199.8398.4398.9198.6498.5998.9798.77Mg#0.870.840.820.870.860.880.810.860.880.880.850.87Cr1026.00515.00303.0087.40260.00381.00279.00837.00446.00397.00469.00397.00Co122.00199.00264.00184.00176.00123.00244.00121.00141.00150.00171.00147.00Ni1941.003256.004401.002663.004029.002564.006917.001885.003365.003931.002016.003369.00Cu162.00371.001010.0097.00556.00153.001777.0079.60347.00394.00290.00329.00Zn68.5065.8066.7095.3083.8065.9089.1071.5060.8064.4094.0073.70Rb8.164.743.991.537.948.102.646.416.872.380.058.37Sr65.9034.1082.7020.9024.8096.6096.6074.4017.3014.906.5918.60Cs1.351.090.740.801.522.910.390.444.301.560.246.33Ba31.3020.1024.9010.8029.1036.820.1030.608.148.563.2810.60Pb4.697.8517.407.125.213.6317.503.005.206.822.533.60Bi0.511.351.281.072.260.342.180.122.242.090.442.00Th0.930.690.460.380.490.660.320.810.300.260.110.27U0.210.320.160.120.180.170.090.170.100.100.050.09Nb0.510.470.620.650.520.520.330.770.280.200.090.25Ta0.060.060.070.140.050.050.050.060.050.050.050.05Zr18.4014.8013.807.0010.7012.2010.1032.607.737.173.158.10Hf0.570.400.430.220.290.340.280.770.220.210.100.23Sb0.060.100.070.140.170.060.170.160.120.100.140.12Ti1543.00889.001226.00623.00527.00768.00815.002298.00700.00503.00300.00663.00V70.4048.4036.2012.6011.9019.0024.5056.5018.0015.3015.2021.30La1.711.561.471.091.162.631.042.220.690.580.300.73Ce4.173.693.922.682.734.752.485.591.651.480.741.74Pr0.550.470.540.330.320.520.320.760.240.180.100.22Nd2.702.152.691.351.542.141.513.601.020.840.461.12Sm0.820.550.670.340.350.480.421.010.300.220.120.28Eu0.230.150.200.090.090.150.170.290.090.06<0.050.11Gd0.940.560.760.300.390.470.471.060.350.290.120.40Tb0.160.090.120.050.060.070.070.190.060.050.050.06Dy0.950.590.790.350.360.430.471.140.370.290.140.38Ho0.210.130.140.060.060.090.100.230.080.060.050.08Er0.600.390.490.220.200.300.310.710.210.180.120.24Tm0.080.050.070.050.050.050.050.090.050.050.050.05Yb0.520.340.440.200.220.250.290.630.200.160.120.23Lu0.080.060.050.050.050.050.050.100.050.050.050.05Sc18.5012.809.325.015.246.347.7813.606.656.135.687.72Y5.723.864.482.052.082.772.867.332.271.721.022.33

圖5　球粒隕石標(biāo)準(zhǔn)化稀土元素分布模式和原始地幔標(biāo)準(zhǔn)化多元素蛛網(wǎng)圖(據(jù)SUN et al., 1989)Fig.5　Chondrite-normalized REE patterns and PM-normalized trace elements spider diagrams(After SUN et al. 1989)

4討論

4.1成巖成礦構(gòu)造背景認(rèn)識

夏日哈木Ⅰ號巖體表現(xiàn)了輕稀土元素相對重稀土元素富集，虧損高場強(qiáng)元素，具有普遍負(fù)Nb異常，推測巖漿作用伴有弧物質(zhì)的卷入(LI et al., 2015；ZHANG et al., 2016)。在鉆孔巖心二輝巖和二輝橄欖巖中，橄欖石Fo值和Ni含量表現(xiàn)了正負(fù)相關(guān)性的兩個(gè)特點(diǎn)，進(jìn)一步表明非一次巖漿成礦作用的結(jié)果。并且橄欖石Fo值在巖體自西向東的剖面中表現(xiàn)了逐漸減小的特點(diǎn)，可能是巖漿流動過程中橄欖巖相結(jié)晶的響應(yīng)，與巖漿流動方向一致。

鎂鐵-超鎂鐵質(zhì)侵入巖及其所含銅鎳硫化物礦床的構(gòu)造背景認(rèn)識對于進(jìn)一步指導(dǎo)區(qū)域找礦具有重要意義(LI et al., 2009；高輝等，2009；張照偉等，2011，2012，2014)。對夏日哈木巖漿銅鎳硫化物礦床礦體上下盤不含礦的鉆孔巖心進(jìn)行鋯石挑選，具體位置是鉆孔ZK5E07S 340～350 m處和鉆孔ZK1501S 330～340 m處的巖心，巖性為非礦化橄輝巖，獲得(412.9±1.8) Ma(MSWD=1.2)和(410.9±1.6) Ma(MSWD=3.1)的諧和年齡，比較一致的年齡信息可代表夏日哈木巖漿銅鎳硫化物礦床含礦巖性的形成時(shí)代(張照偉等，2015b)。宋謝炎等也獲得了夏日哈木巖漿銅鎳硫化物礦床410 Ma鋯石SHRIMP年齡(宋謝炎等，2014)，進(jìn)一步表明青海省東昆侖夏日哈木銅鎳礦床形成于早泥盆世。綜合區(qū)域早泥盆世火山巖組合(玄武安山巖-安山巖-英安巖-流紋巖)，以及廣泛出露的同時(shí)代的花崗巖基，多數(shù)學(xué)者認(rèn)為該地區(qū)的早泥盆世處于碰撞后伸展階段(宋謝炎等，2014)。已有研究認(rèn)為，東昆侖巖漿弧大約形成于450～430 Ma，在昆北造山帶的東部，發(fā)現(xiàn)有形成于428 Ma榴輝巖(MENG et al., 2013；杜瑋等，2015)，其他幾處蛇綠混雜巖的年齡變化為467～518 Ma，并且這些蛇綠混雜巖的玄武質(zhì)巖石具有典型的MORB 特征(牛曉露等，2013，2015；秦克章等，2014)。夏日哈木超鎂鐵巖母巖漿表現(xiàn)了富集輕稀土 、明顯的負(fù)Nb 異常，橄欖石中Ca虧損和高的SiO2含量，表現(xiàn)出了弧巖漿巖的特點(diǎn)(NALDRETT ,2009；MAIER et al., 2010；謝燮等，2014；LI et al., 2015)?；煊谢r漿物質(zhì)的原生巖漿，在上升過程中遭受地殼硫的混染(LI et al., 2015)，導(dǎo)致巖漿中的硫化物達(dá)到飽和，上升的巖漿中充滿了不混溶的硫化物小液滴。盡管表現(xiàn)出了島弧環(huán)境的地球化學(xué)信息，但并非一定就是島弧背景，深部巖漿在上升過程中混染一些其他屬性的地球化學(xué)信息不難理解。夏日哈木鎂鐵-超鎂鐵質(zhì)侵入巖及銅鎳硫化物礦床的形成，可能與柴達(dá)木盆地邊緣裂解巖漿作用關(guān)系密切，是穩(wěn)定陸塊邊緣活動的產(chǎn)物。

圖6　夏日哈木超鎂鐵質(zhì)巖體橄欖石Fo值與Ni含量關(guān)系圖Fig.6　Covariation graph of Fo value vs. Ni content from olivine in Xiarihamu ultramafic intrusion

4.2進(jìn)一步找礦方向

夏日哈木礦區(qū)已發(fā)現(xiàn)5個(gè)鎂鐵-超鎂鐵巖體，但僅Ⅰ號巖體發(fā)育了具有經(jīng)濟(jì)價(jià)值的超大型礦體，其他4個(gè)巖體目前尚未發(fā)現(xiàn)有價(jià)值的礦化線索。究其原因，這5個(gè)鎂鐵-超鎂鐵巖體并非同期同構(gòu)造背景的產(chǎn)物，夏日哈木狹小區(qū)域內(nèi)除含礦的鎂鐵-超鎂鐵巖之外，既有鎂質(zhì)橄欖巖，又有與深俯沖密切相關(guān)的榴輝巖(祁生勝等，2014)，足見該區(qū)域地質(zhì)構(gòu)造背景的復(fù)雜性。夏日哈木Ⅰ號巖體表現(xiàn)了多期次的成礦作用，是深部熔離-多期貫入成礦作用的具體表現(xiàn)，在其深部主要是巖漿來源的方向，存在進(jìn)一步找礦空間與潛力。夏日哈木Ⅱ號巖體，盡管已發(fā)現(xiàn)了少量的硫化物礦化，但巖體主體與旁邊的榴輝巖是何關(guān)系尚不清楚，這也影響了對進(jìn)一步找礦方向的判斷。夏日哈木Ⅲ號巖體、Ⅳ號巖體及Ⅴ號巖體，發(fā)育了鎂質(zhì)橄欖巖，對成銅鎳礦不利。除夏日哈木之外，在柴達(dá)木盆地西北緣發(fā)現(xiàn)了402 Ma牛鼻子梁含礦鎂鐵-超鎂鐵質(zhì)侵入巖體(凌錦蘭等，2014；錢兵等，2015；張照偉等，2015a)，在柴北緣也有類似侵入巖體的發(fā)現(xiàn)，并且伴有較好的鎳礦化，只是成巖成礦時(shí)代尚未確定。這些巖體或者礦床的產(chǎn)出特點(diǎn)就是圍繞柴達(dá)木克拉通周緣的造山帶中，是穩(wěn)定克拉通邊緣的產(chǎn)物。圍繞柴達(dá)木盆地周緣，成巖時(shí)代在412 Ma左右，巖相分異良好的鐵質(zhì)系列鎂鐵-超鎂鐵質(zhì)侵入巖體是下一步重要的勘查對象。

5結(jié)論

(1)青海省夏日哈木鎂鐵-超鎂鐵質(zhì)巖體產(chǎn)出構(gòu)造背景復(fù)雜，巖體成群出現(xiàn)，Ⅰ號巖體表現(xiàn)出了多期次巖漿活動的特點(diǎn)，整體是一次大的巖漿成礦事件，是柴達(dá)木盆地邊緣裂解巖漿活動與成礦作用的具體表現(xiàn)。

(2)夏日哈木Ⅰ號巖體和Ⅱ號巖體的深部具有較好找礦潛力。

(3)在柴達(dá)木盆地南緣東昆侖造山帶內(nèi)，形成時(shí)代約412 Ma，具有明顯巖相分帶鐵質(zhì)系列的鎂鐵-超鎂鐵質(zhì)侵入巖體是下一步勘探尋找銅鎳硫化物礦的重要對象。

致謝：野外地質(zhì)工作得到青海省地質(zhì)調(diào)查局、青海省地礦局、青海省第五地質(zhì)礦產(chǎn)勘查院領(lǐng)導(dǎo)及野外一線工作同志的支持、關(guān)心與幫助；國土資源部巖漿作用成礦與找礦重點(diǎn)實(shí)驗(yàn)室的張江偉、李侃、張志炳、王博林共同參與野外工作及插圖繪制；論文評審專家給予了很好的建議和具體修改意見，在此一致深表感謝。

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收稿日期：2015-06-30；修回日期： 2016-02-19

基金項(xiàng)目：國土資源部公益性行業(yè)科研專項(xiàng)“拉陵灶火鎳成礦賦礦機(jī)理及勘查技術(shù)研究示范”(201511020)和中國地質(zhì)調(diào)查局“東昆侖銅鎳多金屬資源基地調(diào)查”二級項(xiàng)目(DD20160013)共同資助

作者簡介：張照偉(1976-)，男，副研究員，博士，主要從事巖漿銅鎳硫化物礦床成礦理論研究與鎳礦資源調(diào)查評價(jià)工作。E-mail: zhaoweiz@126.com

中圖分類號：P618.41；P618.63

文獻(xiàn)標(biāo)志碼：A

文章編號：1009-6248(2016)02-0045-14

Petrogeochemical Characteristics of the Xiarihamu Magmatic Ni-Cu Sulfide Deposit in Qinghai Province and Its Study for Olivine

ZHANG Zhaowei1, QIAN Bing1, WANG Yalei1, LI Shijin2,LIU Changzheng3

(1.Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, MLR, Xi’an Institute of Geology and Mineral Resources, Xi’an 710054, Shaan Xi, China;2.Qinghai Bureau of Geological Survey, Xining 810028, Qinghai, China;3.No.5 Institute of Geology and Minerals Exploration of Qinghai Province, Xining 810028, Qinghai, China)

Abstract：Located in eastern Kunlun orogenic belt in Qinghai Province, the super-large Xiarihamu magmatic Ni-Cu sulfide deposit is the second ones after Jinchuan Ni-Cu sulfide deposit.Totally, 5 mafic-ultramafic intrusionswere developed 1n this mining area,in which some super-large economic ore-bodies have been found only in No.Ⅰintrusive rocks, but other 4 ones belong to basicto magnesium peridotite and eclogite, these maybe the results of at least two tectonic systems superimposed with magmatic activities. For the No.Ⅰintrusive rocks in the Xiarihamu deposit, their SiO2 contentsvary from 34.11% to 54.28%,and m/f ratios range from 2.01 to 4.93, belonging to ferruginous basic-ultrabasic rocks.The Fo and Ni valuesof olivine show that the Xiarihamu Ni-Cu deposit had experienced multiple stage of magmatic mineralization, the positive and negative correlations between Fo value and Ni content from olivine stand for the immiscibility of sulfide in the early mineralization stage. Combined with regional chronology and other geological information, it’s believed that the Xiarihamu super-large magmatic Ni-Cu sulfide deposit was the result of early lower Devonian magmatism and mineralization in the margin of Qaidam basin, eastern Kunlun orogenic belt. By the way, there maybe have better metallogenic conditions and prospecting potentiality in the depth of No.ⅠandⅡ intrusions, especially the place of magmatic origin or flowing direction, but the other three mafic-ultramafic intrusions that mainly belonged to magnesium peridotite have bad metallogenic condition on Ni-Cu sulfide deposit, and no economic value.

Keywords：petrogeochemical characteristics; mafic-ultramaficintrusions;magmatic Ni-Cu sulfide deposit; exploration direction; Xiarihamu; Qinghai Province