西藏甲玛铜多金属矿含矿斑岩黑云母和角闪石矿物化学特征

张忠坤1,陈国良1,杨征坤1,唐 攀2,高福太1,焦海军1,王志超3,祁 婧3,吴纯能4

(1. 西藏华泰龙矿业开发有限公司, 西藏 拉萨 850200; 2. 西南交通大学 地球科学与环境工程学院, 四川 成都 611756; 3. 中国地质大学(北京) 地球科学与资源学院, 北京 100083; 4. 成都理工大学 地球科学学院, 四川 成都 610059)

摘 要: 甲玛超大型铜多金属矿床位于冈底斯成矿带东段,矿体主要包括矽卡岩型、斑岩型、角岩型和独立金矿体4种类型。矿床中酸性侵入体中广泛发育岩浆黑云母,部分岩体较发育角闪石。本文在全面开展矿区地质调查和详细的钻孔岩芯编录的基础上,对含矿二长花岗斑岩和含矿花岗闪长斑岩中的岩浆黑云母以及含矿花岗闪长斑岩中的角闪石开展了矿物学及矿物化学研究,以揭示其成岩成矿意义。研究结果表明,二长花岗斑岩和花岗闪长斑岩中的岩浆黑云母为镁质黑云母,具有富镁高钛、高铝低硅、富钾贫钠的特点。与花岗闪长斑岩相比,二长花岗斑岩中的岩浆黑云母具有较低的TiO2、FeOT、MgO、MnO、Na2O、BaO含量,较高的Al2O3和SiO2含量。花岗闪长斑岩中的角闪石属于阳起石,具有高硅低铝钛、富镁钙贫钠钾等特征。黑云母和角闪石温度计计算结果显示,含矿二长花岗斑岩中黑云母结晶温度为740.1~783.8℃,平均为762.4℃;含矿花岗闪长斑岩中黑云母结晶温度为750.3~766.9℃,平均为757.2℃;含矿花岗闪长斑岩中角闪石结晶温度为654.1~698.9℃,平均为680.3℃。黑云母和角闪石矿物化学特征指示,二长花岗斑岩和花岗闪长斑岩为造山带钙碱性岩系、Ⅰ型花岗岩,具有壳幔混源的特征。二长花岗斑岩和花岗闪长斑岩具有较高的氧逸度(NNO以上)及水含量,有利于铜、钼等成矿物质进入成矿流体中。

关键词: 角闪石; 黑云母; 矿物化学特征; 甲玛; 西藏

冈底斯成矿带是特提斯成矿域内的一个世界级斑岩-矽卡岩-浅成低温热液型铜钼铅锌多金属成矿带,目前带内已发现评价了多个大型-超大型矿集区,包括雄村铜金矿集区、厅宫-冲江铜矿集区、甲玛-驱龙-邦铺铜钼多金属矿集区等(唐菊兴等, 2010, 2019; 唐攀等, 2016a)。甲玛铜多金属矿床作为冈底斯成矿带东段斑岩成矿系统的典型代表,备受矿床学家或矿床勘查学家的关注,特别是在矿床地质特征(唐菊兴等, 2010; Zheng et al., 2016; 唐攀等, 2017a)、成矿元素分布规律(郑文宝等, 2010)、成岩成矿年代学(应立娟等, 2011)、成矿物质来源(郑文宝等, 2012)、成矿流体来源与演化(周云等, 2011a; 王艺云等, 2017)、控岩控矿构造(钟康惠等, 2012; Duan et al., 2014)以及矽卡岩分带特征(Zheng et al., 2016)等方面取得了一系列显著的研究成果,构建了“四位一体”勘查模型(唐菊兴等, 2011),为指导深部及外围勘查找矿发挥了巨大作用(唐菊兴等, 2013)。目前,已探明各种类型矿体总的铜金属量已超过900万吨,共伴生的钼铅锌金银资源量均达大型以上规模。

黑云母作为斑岩矿床中重要的镁铁质矿物以及指示矿物,其复杂的化学成分可以示踪岩浆、热液过程的物化条件,并指导斑岩铜、钼、金等矿床的找矿勘查(Abdel-Rahman, 1994; Webster, 2004; Siahcheshm et al., 2012; 唐攀等, 2017b; Tang et al., 2019a, 2019b)。角闪石也是斑岩矿床侵入岩中较为常见的镁铁质矿物,能够在宽泛的温压范围内稳定存在(Nandedkar et al., 2014),其主量成分特征不仅可以制约岩浆温度、压力、氧逸度等条件,又能提供岩浆源区等重要成岩信息(姜常义等, 1984; Ridolfi et al., 2010; 吴欢欢等, 2019)。虽然前人对甲玛矿床的研究颇为成熟,但在对甲玛重要的镁铁质造岩矿物学研究方面较为薄弱,仅有王葳平等(2012)和唐攀等(2016b)重点对甲玛矿床的热液黑云母展开了矿物学及矿物化学研究,反演了成矿流体的物理化学条件,但对岩浆黑云母的指示意义研究较少。本文通过对甲玛矿床含矿岩体中的岩浆黑云母和角闪石开展了矿物化学研究,以制约其成岩成矿过程。

1 矿床地质特征

甲玛矿床位于西藏自治区拉萨市墨竹工卡县甲玛乡境内。区内出露地层简单,主要为多底沟组灰岩大理岩(J3d)、林布宗组变质岩(碳质板岩、角岩)(K1l)和第四系残坡积物(图1)。其中,多底沟组灰岩大理岩作为矿床的底板分布在矿体下部,与下覆地层为不整合接触,主要分布于矿区铜山-铅山一带以及北西部的牛马塘一带。林布宗组碳质板岩和角岩作为矿床的顶板分布在矿体上部,与下覆多底沟组呈整合接触,主要分布于矿区的中-北部广大区域。第四系主要是一些残坡积层、冲积层,由砂、砾石、粉质粘土、亚粘土组成,多分布于矿区北西部的夏工普沟等山前坡地、冲沟及低洼处。

图1 甲玛矿区地质简图[据林彬等(2019)修改]
Fig. 1 Geological map of Jiama deposit (modified after Lin Bin et al., 2019)

1—第四系沉积物; 2—下白垩统林布宗组砂、板岩、角岩; 3—上侏罗统多底沟组灰岩、大理岩; 4—花岗闪长斑岩脉; 5—花岗斑岩脉; 6—细晶岩脉; 7—矽卡岩化大理岩; 8—矽卡岩矿体; 9—钻孔; 10—铜山滑覆构造; 11—甲玛-卡军果逆冲推覆构造; 12—矿段范围; 13—取样位置

1—Quaternary sedimentary rocks; 2—sandstone, slate and hornfels of Linbuzong Formation in lower Cretaceous; 3—limestone and marble of Duodigou Formation in Upper Jurassic; 4—granodiorite porphyry veins; 5—granite porphyry veins; 6—aplite veins; 7—skarn marble; 8—skarn orebody; 9—drill hole; 10—Tongshan slip fault; 11—Jiama-Kajunguo thrust-gliding nappe tectonic; 12—segment of mining; 13—sampling location

构造对甲玛斑岩铜多金属矿系统的形成至关重要。甲玛铜多金属矿床受控于甲玛-卡军果逆冲推覆构造系和铜山滑覆构造。其中,甲玛-卡军果逆冲推覆构造主要指矿区由北向南“叠缩式”的逆冲推覆褶皱带,控制着甲玛矿区Ⅰ号矽卡岩主矿体的产出状态。而铜山滑覆构造属于整个推覆构造体系的重要组成部分,主要指矿区东南部铜山—布朗沟—莫古郎沟一带,受推覆形成的铜山高位岩块,由于重力失稳而反向滑覆形成的滑覆构造体以及次级褶皱和裂隙,该滑覆构造控制着矿区内Ⅱ号矽卡岩矿体的产出状态(唐攀等, 2017a)。

甲玛矿区岩浆岩地表出露面积较小,以中酸性岩浆活动为主,多呈隐伏岩枝侵位。岩石类型主要为中新世中酸性侵入岩,局部有少量的基性岩脉。其中,中酸性侵入岩主要包括花岗闪长斑岩、二长花岗斑岩、花岗斑岩、石英闪长玢岩、闪长玢岩。其中,二长花岗斑岩、花岗斑岩与钼矿化密切相关,而花岗闪长斑岩、部分石英闪长玢岩则与铜矿化密切相关。基性岩脉主要为暗色煌斑岩细脉以及矿区外围产出的少量辉绿岩脉。

甲玛斑岩成矿系统由不同容矿围岩空间中多种矿体组成,即产在斑岩体顶部的角岩型铜钼矿体+中部矽卡岩型铜多金属矿体+深部的隐伏斑岩型钼铜矿体+矿区外围产于构造破碎带中的独立金矿体,构成特有的“四位一体”矿体组成格局(图2)。

图2 甲玛矿床矿体结构剖面图[据邹兵等(2019)修改]
Fig. 2 Profile of orebodies in the Jiama deposit (modified after Zou Bing et al., 2019)

1—林布宗组砂、板岩、角岩; 2—多底沟组灰岩、大理岩; 3—花岗闪长斑岩; 4—二长花岗斑岩; 5—石英闪长玢岩; 6—闪长玢岩; 7—角岩矿体; 8—矽卡岩矿体; 9—矽卡岩化大理岩; 10—独立金矿体; 11—钻孔; 12—铜山滑覆构造

1—sandstone, slate and hornfels of Linbuzong Formation; 2—limestone and marble of Duodigou Formation; 3—granodiorite porphyry; 4—monzogran-ite porphyry; 5—quartz diorite porphyrite; 6—diorite porphyrite ; 7—hornfels orebody; 8—skarn orebody; 9—skarn marble; 10—Au orebody; 11—drill hole; 12—Tongshan slip fault

甲玛矿区热液蚀变主要为钾化、绢英岩化、泥化、青磐岩化和矽卡岩化。钾化主要为黑云母化,发育于含矿斑岩体及其接触部位的角岩中,矿物组合主要为黑云母、石英等。绢英岩化主要发育角岩中的钾化蚀变上部以及一些斑岩脉中,矿物组合主要为绢云母、石英、黄铁矿等。泥化发育于角岩顶部和一些斑岩脉中,矿物组合主要为高岭石、绢云母。青磐岩化发育于钾化和绢英岩化的外围,矿物组合主要为绿泥石、方解石、黄铁矿及少量的绿帘石。矽卡岩化发育于斑岩体接触带、大理岩和角岩中,矿物组合主要为石榴子石、硅灰石、透辉石、绿泥石和绿帘石等。

2 黑云母和角闪石矿物学特征

二长花岗斑岩和花岗闪长斑岩广泛发育岩浆黑云母,矿物学特征类似。在偏光显微镜下,岩浆黑云母呈斑晶产出,自形-半自形,片状,粒径为0.2~1 mm,常见一组的极完全解理,多色性显著,不同光率体方位黑云母晶体颜色变化于深褐色-浅黄色之间,常被后期的绿泥石沿其解理或边缘交代(图3)。黑云母自形程度高,单个晶体的干涉色均一,且常包裹早期结晶的磷灰石、磁铁矿等矿物,具有岩浆成因特征,区别于热液黑云母矿物学特征(Luan et al., 2014; 向坤等, 2019)。甲玛矿床热液黑云母呈极细-细的片状或少量的片状集合体产出,半自形-它形,粒径一般小于0.2 mm(王葳平等, 2012; 唐攀等, 2016b),明显不同于岩浆黑云母矿物学特征。

图3 甲玛矿床二长花岗斑岩和花岗闪长斑岩中岩浆黑云母镜下特征
Fig. 3 Photomicrographs of magmatic biotite in monzogranite porphyry and granodiorite porphyry from the Jiama deposit

a—二长花岗斑岩中岩浆黑云母被后期的绿泥石交代; b—二长花岗斑岩中的岩浆黑云母; c—花岗闪长斑岩中的岩浆黑云母被后期的绿泥石交代,包裹早期的磷灰石、磁铁矿; d—花岗闪长斑岩中的岩浆黑云母; Bt—黑云母; Chl—绿泥石; Ap—磷灰石; Mt—磁铁矿

a—magmatic biotite in monzogranite porphyry replaced by chlorite; b—magmatic biotite in monzogranite porphyry; c—magmatic biotite in granodiorite porphyry replaced by chlorite and wrapping early apatite and magnetite; d—magmatic biotite in granodiorite porphyry; Bt—biotite; Chl—chlorite; Ap—apatite; Mt—magnetite

二长花岗斑岩中未见角闪石,花岗闪长斑岩中角闪石含量较少,主要以斑晶形式产出,镜下观察纵切面呈长柱状,粒径为0.3~1 mm,横截面可见菱形,呈自形-半自形产出,横截面易见两组完全解理,夹角56°,多色性比较明显,变化于浅绿-浅黄绿之间,常被后期的绿泥石和热液黑云母交代(图4)。

图4 甲玛矿床花岗闪长斑岩中角闪石镜下特征
Fig. 4 Photomicrographs of hornblende in granodiorite porphyry from the Jiama deposit

Hb—角闪石; Bt—黑云母; Chl—绿泥石

Hb—hornblende; Bt—biotite; Chl—chlorite

3 取样与分析测试

3.1 样品采集与实验方法

本次样品主要采自24号勘探线ZK2417、ZK2414、ZK2412和ZK2409(1个角闪石样品采自ZK2010)钻孔中的花岗闪长斑岩和二长花岗斑岩,详细采样位置见图1和表1、表2(样品编号为钻孔+采样深度+测试点号)。黑云母样品采自花岗闪长斑岩和二长花岗斑岩;角闪石样品采自花岗闪长斑岩,二长花岗斑岩未见角闪石。

所采集的花岗闪长斑岩为中粒斑状结构,斑晶含量约30%~50%,主要为石英(0.5~4 mm)和斜长石(0.5~40 mm),有少量的黑云母(0.2~1 mm)、钾长石(1~40 mm)和角闪石(0.3~1 mm);基质主要为长英质,包括石英、斜长石等。副矿物主要为磷灰石、锆石、金红石和榍石。蚀变主要为黑云母化和绢英岩化。

所采集的二长花岗斑岩为中粒斑状结构,斑晶含量约35%~50%,主要为石英(1~3 mm)、斜长石(0.5~40 mm)和钾长石(1~40 mm),有少量的黑云母(0.2~1 mm);基质主要为长英质,包括石英、斜长石等。副矿物主要为磷灰石、锆石、金红石和榍石。蚀变主要为黑云母化和绢英岩化。

通过镜下光薄片鉴定,选取蚀变较弱的黑云母和角闪石,在天津地质调查中心实验室进行了电子探针测试。实验仪器为日本岛津公司生产的EPMA-1600型电子探针分析仪,加速电压15 kV,电流20 nA,束斑直径10 μm。主量元素的允许相对误差小于2%。以下天然矿物作为标定矿物:磷灰石(P、Ca)、石英(Si)、萤石(F)、硅铍铝钠石(Cl)、硬玉(Na)、镁铝榴石(Mn)、磁铁矿(Fe)、钛铁矿(Ti)、钾长石(K)。

3.2 分析结果

甲玛矿床含矿斑岩中岩浆黑云母结构式基于22个氧原子计算获得,Fe3+和Fe2+采用林文蔚等(1994)方法计算,OH=4-F-Cl。花岗闪长斑岩中角闪石的离子数计算采用Ridolfi 等(2018)提出的AMFORM——一种新的基于质量平衡的角闪石单元式计算模型,该模型相比以往计算方法经过验证误差更小,与高精结构实验测试结果拟合近1∶1,效果更好,并且针对原生和经氧化蚀变的角闪石都有对应的公式用以计算不同占位的阴阳离子数。黑云母和角闪石的化学成分分析数据分别见表1、表2。

表1 甲玛矿床典型岩浆黑云母电子探针分析数据 wB/%
Table 1 Representative electron microprobe analyses of magmatic biotite at the Jiama deposit

岩性二长花岗斑岩花岗闪长斑岩样品2414-138-22414-145-12414-147-12414-147-112414-157-12414-152-22412-145-12412-145-22412-145-32417-511-12417-511-22417-511-3SiO238.73 38.52 38.42 38.27 37.84 38.05 38.07 38.62 37.96 36.37 37.44 36.75 Al2O315.15 14.67 14.82 14.29 14.13 14.51 12.47 12.71 12.77 12.12 12.96 12.41 TiO23.26 3.49 3.82 3.36 3.80 3.94 3.97 3.82 3.90 4.04 3.92 4.04 FeOT9.18 13.00 8.92 10.72 11.08 11.53 13.28 14.42 14.10 16.19 14.76 14.86 MnO0.07 0.09 0.06 0.06 0.25 0.06 0.20 0.13 0.11 0.22 0.17 0.21 MgO15.64 13.92 15.51 14.78 15.13 14.26 16.90 16.88 16.50 14.07 15.66 15.27 BaO0.14 0.36 0.25 0.13 0.33 1.71 0.48 0.60 0.16 0.91 0.76 0.76 CaO0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 Na2O0.13 0.13 0.14 0.16 0.10 0.12 0.41 0.51 0.38 0.30 0.39 0.27 K2O8.88 8.73 8.74 8.75 8.71 8.69 8.24 8.29 8.66 8.62 8.60 8.83 F1.46 0.68 1.38 1.00 0.72 0.58 0.80 0.63 0.52 0.81 0.66 0.82 Cl0.09 0.13 0.08 0.08 0.08 0.09 0.06 0.09 0.09 0.02 0.03 0.04 CuO0.00 0.00 0.00 0.00 0.06 0.04 0.02 0.04 0.00 0.00 0.03 0.02 O=F,Cl0.63 0.32 0.60 0.44 0.32 0.26 0.35 0.28 0.24 0.34 0.28 0.35 H2Ocalc3.22 3.61 3.24 3.40 3.56 3.65 3.59 3.73 3.73 3.45 3.65 3.49 Total96.58 97.64 95.96 95.43 96.10 97.48 98.85 100.75 99.12 97.45 99.29 98.10 Si5.90 5.82 5.88 5.89 5.79 5.78 5.73 5.71 5.69 5.68 5.66 5.67 AlⅣ2.10 2.18 2.12 2.11 2.21 2.22 2.21 2.22 2.25 2.23 2.31 2.26 T Site8.00 8.00 8.00 8.00 8.00 8.00 7.95 7.93 7.94 7.92 7.97 7.92 AlⅥ0.62 0.43 0.55 0.48 0.33 0.37 0.00 0.00 0.00 0.00 0.00 0.00 Ti0.37 0.40 0.44 0.39 0.44 0.45 0.45 0.43 0.44 0.48 0.45 0.47 Fe3+0.24 0.32 0.24 0.28 0.28 0.29 0.28 0.29 0.28 0.30 0.29 0.28 Mn0.01 0.01 0.01 0.01 0.03 0.01 0.03 0.02 0.01 0.03 0.02 0.03 Mg3.55 3.14 3.54 3.39 3.45 3.23 3.79 3.72 3.68 3.28 3.53 3.51 Fe2+0.92 1.33 0.90 1.10 1.14 1.17 1.39 1.50 1.49 1.81 1.58 1.64 O Site5.72 5.62 5.68 5.65 5.66 5.52 5.94 5.95 5.91 5.90 5.86 5.92 Na0.04 0.04 0.04 0.05 0.03 0.04 0.12 0.15 0.11 0.09 0.11 0.08 K1.73 1.68 1.71 1.72 1.70 1.68 1.58 1.56 1.66 1.72 1.66 1.74 Ca0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Ba0.01 0.02 0.01 0.01 0.02 0.10 0.03 0.03 0.01 0.06 0.05 0.05 A Site1.76 1.72 1.75 1.77 1.73 1.72 1.70 1.71 1.77 1.81 1.77 1.82 F0.70 0.33 0.67 0.48 0.35 0.28 0.38 0.29 0.25 0.40 0.31 0.40 Cl0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 OH3.28 3.64 3.31 3.49 3.63 3.70 3.61 3.69 3.73 3.60 3.68 3.59 XMg0.62 0.56 0.62 0.60 0.61 0.58 0.64 0.63 0.62 0.56 0.60 0.59 XFe0.33 0.40 0.32 0.35 0.34 0.36 0.31 0.32 0.32 0.39 0.35 0.35 t/℃763.6 740.1 783.8754.3767.7764.9766.9754.7758.7750.3754.2758.6logfO2-15.15 -15.75 -14.65 -15.38 -15.04 -15.11 -15.06 -15.37 -15.27 -15.48 -15.38 -15.27 Fe2+/(Fe2++Mg)0.210.300.200.240.250.270.270.290.290.360.310.32

3.2.1 黑云母

甲玛矿床含矿二长花岗斑岩和花岗闪长斑岩中岩浆黑云母CaO含量大部分检测为0.00%(1个值为0.01%),指示样品未受大气降水或绿泥石化或碳酸盐化的影响(Kumar and Pathak, 2010)。另外黑云母的Fe2+/(Fe2++Mg)值介于0.20~0.36之间,均值0.27,标准差0.04,比较均一,也指示样品几乎未受后期的热液流体改造(Stone, 2000)。唐攀(2018)研究表明,甲玛矿床热液黑云母BaO和TiO2含量较低, BaO含量一般小于0.1%,TiO2含量一般小于3%。本研究中黑云母样品具有较高的BaO和TiO2含量,Ti离子数为0.37~0.48, TiO2含量为3.26%~4.04%,BaO含量为0.14%~1.71%。甲玛矿床岩浆黑云母矿物学特征和成分特征明显不同于热液黑云母,岩浆黑云母通常为自形-半自形,粒径较大(一般大于0.2 mm),包裹早期结晶的磷灰石、磁铁矿等矿物,具有较高的BaO和TiO2含量、较低的CaO含量以及较均一的Fe2+/(Fe2++Mg)值。

根据国际矿物学协会(IMA)对黑云母的分类,甲玛矿床含矿二长花岗斑岩和花岗闪长斑岩中岩浆

表 2 甲玛矿床典型角闪石电子探针分析数据 wB/%
Table 2 Representative electron microprobe analyses of hornblende at the Jiama deposit

样品2010-564-32010-564-42409-383-12409-402-1SiO254.01 54.88 53.35 54.29 TiO20.22 0.23 0.21 0.12 Al2O32.33 2.03 1.54 1.29 FeOT10.49 9.69 9.16 10.00 MnO0.36 0.36 0.11 0.15 MgO18.13 18.57 18.02 17.17 CaO11.90 12.20 11.38 12.22 Na2O0.77 0.61 0.61 0.63 K2O0.26 0.24 0.20 0.20 BaO0.00 0.00 0.00 0.00 F0.35 0.44 0.23 0.08 Cl0.03 0.05 0.03 0.03 CuO0000.05 Total98.85 99.29 94.83 96.23 Si7.60 7.66 7.72 7.84 Al0.39 0.33 0.26 0.16 Ti0.02 0.01 0.02 0.00 sum T8.00 8.00 8.00 8.00 Al0.00 0.00 0.00 0.06 Ti0.01 0.02 0.00 0.01 Fe3+0.37 0.35 0.52 0.07 Mg3.80 3.86 3.88 3.70 Fe2+0.87 0.78 0.59 1.14 Mn0.04 0.04 0.01 0.02 sum C5.08 5.05 5.01 5.00 Ca1.79 1.82 1.76 1.89 Na 0.13 0.13 0.17 0.11 sum B1.92 1.95 1.93 2.00 Ca0.00 0.00 0.00 0.00 Na0.09 0.04 0.00 0.07 K0.05 0.04 0.04 0.04 sum A0.13 0.08 0.04 0.11 ΔNNO2.88 2.96 3.08 2.66 t/℃698.92 687.06 681.06 654.12 logfO2-13.50 -13.74 -13.78 -14.95

黑云母样品均落于镁质黑云母范围内(图5)。与Kahang、Sarcheshmeh、Dalli、Darreh-Zar、Miduk、拉抗俄、邦铺、雄村等斑岩铜多金属矿床一样(Ayati et al., 2008; Boomeri et al., 2009, 2010; Afshooni et al., 2013; Parsapoor et al., 2015; 唐攀等, 2017b; Tang et al., 2019b; 肖鸿天等, 2020),甲玛矿床岩浆黑云母也具有富镁的特征。

图5 甲玛矿区含矿斑岩中黑云母分类图解(底图据Foster, 1960)
Fig. 5 Mg-(Al+Fe3++Ti)-(Fe2++Mn) ternary classification of biotites (after Foster, 1960)

a—金云母; B—镁质黑云母; C—铁质黑云母; D—铁叶云母; E—铁白云母; F—白云母

a—phlogopite; B—magnesian biotite; C—ferrobiotite; D—siderophyllite; E—ferro-muscovite; F—muscovite

黑云母成分与XMg的协变图解见图6。二长花岗斑岩中的黑云母主量成分相对集中,而花岗闪长斑岩中的相对分散;与花岗闪长斑岩中的黑云母相比,二长花岗斑岩中的黑云母的TiO2、FeOT、MgO、MnO和Na2O含量相对较低,而Al2O3和SiO2含量较高。总体上,两种含矿斑岩中的黑云母具有富镁高钛、高铝低硅、富钾贫钠的特点。

图6 甲玛矿床岩浆黑云母的XMg-SiO2、K2O、TiO2、Al2O3、FeOT、MnO、BaO、Na2O图解
Fig. 6 Composition of magmatic biotite in the Jiama deposit on XMg -SiO2, K2O, TiO2, Al2O3, FeOT, MnO, BaO and Na2O plots

3.2.2 角闪石

含矿花岗闪长斑岩中角闪石主要成分显示以下基本特征: SiO2含量高(53.35%~54.88%),Al2O3、TiO2含量低(1.29%~2.33%、0.12%~0.22%),MgO含量高(17.17%~18.57%),全铁(FeOT)较低(9.16%~10.49%),MnO含量为0.11%~0.36%,CaO含量高(11.38%~12.22%),Na2O、K2O含量低(0.61%~0.77%、0.20%~0.26%),BaO含量低于检出限,F、Cl含量分别为0.08%~0.44%、0.03%~0.05%(表2),总体具有高硅低铝钛、富镁钙贫钠钾等特征。

角闪石(Ca+Na)B值为1.92~2.00,且NaB为0.11~0.17,CaB为1.76~1.89,符合Leake等(1997)提出的角闪石化学分类原则中钙质角闪石要求[(Ca+Na)B ≥l,且NaB<0.50,一般CaB>1.50],属于钙质角闪石亚族,进一步根据其(Na+K)A值0.04~0.13(满足<0.5的要求),最后结合Mg/(Mg+Fe2+)-Si图解(图7),判断含矿花岗闪长斑岩中的角闪石均属于阳起石。

图7 甲玛矿床角闪石分类图(底图据Leake et al., 1997)
Fig. 7 Classification of hornblende in the Jiama depsoit (base diagram after Leake et al., 1997)

4 讨论

4.1 成岩指示意义

4.1.1 结晶温度与氧逸度

基于Henry等(2005)提出的黑云母Ti含量温度计公式,计算出二长花岗斑岩中黑云母结晶温度为740.1~783.8℃,平均值为762.4℃(图8);花岗闪长斑岩中黑云母结晶温度为750.3~766.9℃,平均值为757.2℃(图8),与二长花岗斑岩中黑云母结晶温度类似。利用Ridolfi 等 (2010)的方法估算花岗闪长斑岩中角闪石的形成温度为654.1~698.9℃,平均值为680.3℃,略低于黑云母结晶温度。黑云母和角闪石结晶温度与周云等(2011b)测定的含矿斑岩石英斑晶中熔融包裹体均一温度(630~880℃)类似。

图8 甲玛矿床黑云母的Ti-Mg/(Mg+Fe)图解(底图据Henry et al., 2005)
Fig. 8 Plot of Ti-Mg/(Mg+Fe) for biotites in the Jiama depsoit (base diagram after Henry et al., 2005)

Wones和Eugster(1965)研究表明,黑云母的Fe3+-Fe2+-Mg三角图解可判断结晶环境的相对氧逸度。甲玛矿床二长花岗斑岩和花岗闪长斑岩中的黑云母全部落于HM(Fe2O3-Fe3O4)与NNO(Ni-NiO)氧逸度缓冲剂之间,偏NNO缓冲线一侧(图9a),说明了其结晶环境具有较高的氧逸度,且log fO2>NNO+1。利用公式log fO2=10.9-2 700/T(K)估算黑云母结晶氧逸度(David and Hans, 1965),结果二长花岗斑岩log fO2=-15.75~-14.65,平均值为-15.18;花岗闪长斑岩log fO2=-15.48~-15.06,平均值为-15.31,二者氧逸度类似。张聚全等(2018)研究表明,氧逸度是影响中酸性岩浆岩中黑云母的Fe/(Fe+Mg)值的主要因素,与全岩的Fe/Mg值无关。二长花岗斑岩和花岗闪长斑岩中的黑云母投于(Fe/Fe+Mg)-Al图解(图9b)上,指示其氧逸度范围为FMQ+2.4fO22+/(Fe2++Mg)-Al图解的高氧逸度区域(图10)。黑云母和角闪石氧逸度计均指示二长花岗斑岩和花岗闪长斑岩形成于较高的氧逸度环境中。

图9 甲玛矿床黑云母Fe3+-Fe2+-Mg三角图解(a, 底图Wones and Eugster, 1965)和Fe/(Fe+Mg)-Al图解(b, 底图据Anderson et al., 2008)
Fig. 9 Plot of Fe3+-Fe2+-Mg for biotites (a, base diagram after Wones and Eugster, 1965) and Fe/(Fe+Mg)-Al(b, base diagram after Anderson et al., 2008) for biotites in the Jiama deposit

图10 甲玛矿床角闪石Fe2+/(Fe2++Mg)-Al图解(底图据Dada, 2013)
Fig. 10 Plot of Fe2+/(Fe2++Mg)-Al for hornblendes in the Jiama deposit ( base diagram after Dada, 2013)

4.1.2 岩石成因和构造环境

Abdel-Rahman(1994)研究指出,S、A和Ⅰ型花岗岩中的黑云母分别具有相对高的铝、铁和镁含量;徐克勤等(1984)指出黑云母的MF值[MF=Mg/(Mg+Fe2++Fe3++Mn)]<0.38反映寄主花岗岩为改造型,反之为同熔型(Ⅰ型); 徐克勤等(1986)提出,Ⅰ型花岗岩中的黑云母Mg#值较高(0.384~0.626),氧化系数较高(0.121~0.252)。二长花岗斑岩和花岗闪长斑岩中的岩浆黑云母均属于富镁黑云母(MgO含量14.07%~16.90%),MF值为0.64~0.75,均高于改造型,且Mg#值[Mg#=Mg/(Mg+Mn+Fe2+)]和氧化系数[Fe3+/(Fe3++Fe2+)]均较高,分别为0.64~0.80和0.14~0.21,指示二长花岗斑岩和花岗闪长斑岩为Ⅰ型花岗岩。张东阳等(2009)研究指出,角闪石的低Ti(离子数<0.5)、高Mg/(Mg+Fe)值(0.44~0.70)特征指示寄主岩为Ⅰ型花岗岩。甲玛矿床花岗闪长斑岩角闪石Ti离子数较低(0.01~0.02),Mg/(Mg+Fe)值(0.75~0.78)较高,同样指示花岗闪长斑岩具有Ⅰ型花岗岩特征。Whalen和Chappell(1988)研究表明S型花岗岩中黑云母的Al值范围0.353~0.561,Ⅰ型花岗岩中的Al值<0.224。花岗闪长斑岩中的黑云母Al值均为0,符合Ⅰ型;但是二长花岗斑岩中黑云母Al值范围0.33~0.62,并不符合Ⅰ型花岗岩的特征,可能是后期热液蚀变改造了黑云母中Al成分。

丁孝石(1988)通过对西藏中南部地区黑云母标型的研究指出,幔源岩体中黑云母MgO>15%,而壳源岩体中黑云母MgO<6%。二长花岗斑岩和花岗闪长斑岩中黑云母MgO含量为14.07%~16.90%,指示具有壳幔混源的特征。二长花岗斑岩和花岗闪长斑岩中黑云母投于FeOT/ (FeOT+MgO)-MgO图解上的壳幔混源区(图11a),同样指示壳幔混源的特征。

姜常义等(1984)通过搜集全球具有代表性的271组钙质角闪石成分数据指出,幔源角闪石的Si/(Si+Ti+Al)值≤0.765。谢应雯等(1990)提出角闪石Mg#可用来区分花岗岩的来源类型,幔源型Mg#>0.7,壳幔混合型0.7>Mg#>0.5,壳源型Mg#<0.5。甲玛花岗闪长斑岩中角闪石Si/(Si+Ti+Al)为0.95~0.97,显示非幔源特征;Mg#值为0.77~0.87,指示幔源特征;投于TiO2-Al2O3图解的壳源区域(图12a),但在CaB-(Fe2++Fe3+)-Mg图解的幔源区域(图12b)。这可能是后期热液蚀变改造了角闪石的成分。

图11 甲玛矿床黑云母FeOT/ (FeOT+MgO)-MgO图解(a, 底图据Abdel-Rahman, 1994)和FeOT-MgO-Al2O3图解(b, 底图据周作侠,1986)
Fig. 11 Plot of FeOT/ (FeOT+MgO)-MgO for biotites (a, base diagram after Abdel-Rahman, 1994) and FeOT-MgO-Al2O3 for biotites (b, base diagram after Zhou, 1986) in the Jiama deposit

图12 甲玛矿床角闪石TiO2-Al2O3图解(a, 底图据姜常义等, 1984)和CaB-(Fe2++Fe3+)-Mg图解(b, 底图据谢应雯等, 1990)
Fig. 12 Plot of TiO2-Al2O3 for hornblendes (a, base diagram after Jiang Changyi et al., 1984) and CaB-(Fe2++Fe3+)-Mg for hornblendes (b, base diagram after Xie Yingwen et al., 1990) in the Jiama deposit

二长花岗斑岩和花岗闪长斑岩中黑云母投于MgO-FeOT-Al2O3构造判别图解的造山带钙碱性岩系(图11b)。花岗闪长斑岩中角闪石同样投于KA-Al图解中的钙碱性区域(图13),与黑云母指示结果一致。

图13 甲玛矿床角闪石KA-Al图解(底图据Ridolfi和Renzulli, 2012)
Fig. 13 Plot of KA-Al for hornblendes in the Jiama depsoit (base diagram after Ridolfi and Renzulli, 2012)

甲玛矿区中酸性岩浆岩的地球化学特征及Sr-Nd-Pb同位素指示,二长花岗斑岩与花岗闪长斑岩属于造山带钙碱性岩系、Ⅰ型花岗岩,并具有壳幔混源特征(秦志鹏, 2010, 2013)。张泽斌等(2019)根据甲玛矿床含矿斑岩中的暗色包体主微量及锆石Hf同位素分析结果,认为含矿斑岩为镁铁质岩浆与加厚新生下地壳部分熔融形成的中酸性岩浆发生混合的产物。本文角闪石和黑云母矿物化学特征指示,含矿二长花岗斑岩和花岗闪长斑岩属于造山带钙碱性岩系、I型花岗岩,具有壳幔混源的特征,与前人岩石地球化学及同位素研究结果基本一致。

4.2 成矿指示意义

4.2.1 矿物化学成分指示成矿

黑云母的含铁指数f[f=(Fe2++Fe3+)/(Fe2++Fe3++Mg)]与岩体的矿化类型有关: 低含铁指数者(f=0.05~0.15)常见于含金刚石的金伯利岩;中含铁指数者(f=0.22~0.42)主要产于铜钼、金矿化岩体;较高含铁指数者(0.28~0.52)与铁矿化有关;更高者(0.52~0.92)与钨矿化有关(周作侠, 1986)。甲玛矿床二长花岗斑岩和花岗闪长斑岩中的黑云母含铁指数f位于0.24~0.39区间内,与实际铜钼矿化吻合。

傅金宝(1981)研究指出,含矿岩体的岩浆黑云母特征为:富Mg低Fe,Mg/Fe值一般>0.5;含Ti高, TiO2>3%;具有低铝特征, Al2O3<15%;高K、低Na和Ca为特点, CaO<0.5%,K/Na值多>10。

甲玛矿床二长花岗斑岩和花岗闪长斑岩中的黑云母富镁,Mg/Fe值普遍大于1(1.55~3.10),TiO2含量较高(3.26%~4.04%),Al2O3含量位于12.12~15.15%区间内,CaO含量极低,K/Na值位于10.69~56.19区间内,指示巨大的成矿潜力。

赵一鸣等(2012)提供了不同矿种的矽卡岩型矿床的岩浆黑云母矿物化学特征。甲玛矿床二长花岗斑岩和花岗闪长斑岩中的黑云母铝度为0.16~0.20,碱度为0.65~0.81,均位于矽卡岩型铜矿母岩黑云母对应范围(0.149 8~0.226 4、 0.618 6~0.974 9)内(赵一鸣等, 2012),也指示良好的矽卡岩铜矿成矿潜力。

吕志成等(2003)对大兴安岭地区与两类不同矿种有关的岩体中的角闪石特征进行了对比研究得出,与铜矿化相关的岩浆环境下结晶的角闪石具有富镁(MgO平均含量为6.11%)、硅(SiO2平均含量为51.30%)、钙(CaO平均含量为11.87%)以及相对贫铁(FeOT平均含量为19.05%)的特征,且Mg#值较高,平均值为0.37。甲玛矿床花岗闪长斑岩角闪石镁、硅、钙含量高,对应氧化物平均含量分别为17.97%、54.13%、11.92%;全铁氧化物相对较低,平均为9.84%;Mg#值平均为0.82,显示铜矿化特征。

综上所述,黑云母和角闪石是甲玛铜多金属矿床有效的含矿指示性矿物。

4.2.2 水含量、氧逸度与成矿

利用Ridolfi等(2010)提出的角闪石成分估算岩浆水含量方法,甲玛矿床含矿岩浆水含量为2.79%~3.04%。与驱龙、拉抗俄等斑岩铜钼矿床类似,甲玛矿床含矿斑岩富含黑云母和角闪石等富水矿物,指示其岩浆环境是相对富水的。岩浆富水是斑岩矿床形成的关键(Lu et al., 2015; 侯增谦等, 2020)。富水的岩浆一方面可以降低源区内岩石的熔融温度,从而使富铜新生下地壳中的含铜硫化物再活化(Wang et al., 2014),富集进入含矿岩浆中;另一方面,岩浆中的大量水可以使源区母岩浆具有较高的氧逸度(Richards, 2003)。与贫水岩浆相比,富水岩浆更容易达到水饱和,因此,富水岩浆有利于出溶挥发分,并与铜、钼等成矿物质形成络合物进行远距离运移,在浅地表富集成矿。

高氧逸度是斑岩型铜矿床有利条件之一,尤其是大型、超大型斑岩铜矿的形成与较高的氧逸度条件密切相关(Richards, 2003)。要形成斑岩矿床,尤其是巨型斑岩矿床,需要较高的氧逸度条件,这样在早期的岩浆结晶过程中S能够更多地以高价态形式溶于硅酸盐熔体中,Cu、Mo避免过早、过多地与S2-结合形成早期硫化物,多与络合并残留在熔体相,进一步富集在演化岩浆中,为后期成矿流体的形成提供原料(Sun et al., 2015; Shen et al., 2015)。Mengason等(2011)研究表明,岩浆氧逸度影响Mo的价态,log fO2≥NNO时大部分Mo以的形式存在,避免在早期含Fe、Ti矿物结晶时进入矿物替代Ti,也能避免形成MoS2,因而也有利于Mo在残留岩浆中的富集。Shen等(2015)的研究揭示出岩浆氧逸度与斑岩矿床规模之间存在一定相关性。当氧逸度≥NNO+1时可形成斑岩铜矿(铜<1 Mt);达到NNO+2时,有潜力形成大型-超大型斑岩矿床(铜>2 Mt)。

甲玛矿床含矿斑岩的岩浆黑云母投点于NNO与HM缓冲剂之间,氧逸度绝对值估算范围-15.75~-14.65;角闪石投点于高氧逸度区域内,估算的氧逸度条件ΔNNO≈3,对应绝对值范围-13.78~-13.5,黑云母和角闪石成分均指示甲玛含矿斑岩具有较高氧逸度。在高氧逸度条件下,铜、钼等成矿物质不易进入早期结晶的矿物相中,而富集于熔体相中,进而被后期岩浆出溶的热液流体萃取富集,形成的富含成矿物质的流体,最终在有利的围岩及容矿空间中形成甲玛超大型铜多金属矿床。

5 结论

(1) 甲玛矿床含矿二长花岗斑岩和花岗闪长斑岩中的岩浆黑云母为镁质黑云母,具有富镁高钛、高铝低硅、富钾贫钠的特点。含矿花岗闪长斑岩中角闪石属于阳起石,具有高硅低铝钛、富镁钙贫钠钾等特征。

(2) 含矿二长花岗斑岩中黑云母结晶温度为740.1~783.8℃,平均为762.4℃;含矿花岗闪长斑岩中黑云母结晶温度为750.3~766.9℃,平均为757.2℃;含矿花岗闪长斑岩中角闪石结晶温度为654.1~698.9℃,平均值680.3℃。

(3) 黑云母和角闪石矿物化学特征指示,二长花岗斑岩和花岗闪长斑岩为造山带钙碱性岩系、Ⅰ型花岗岩,具有壳幔混源的特征。

(4) 黑云母和角闪石矿物成分可以有效地指示甲玛斑岩成矿。二长花岗斑岩和花岗闪长斑岩具有较高的氧逸度(NNO以上)及水含量,有利于铜、钼等成矿物质进入成矿流体中。

References

Abdel-Rahman A M. 1994. Nature of biotites from alkaline, calc-alkaline, and peraluminous magmas[J]. Journal of Petrology, 35: 525~541.

Afshooni S Z, Mirnejad H, Esmaeily D, et al. 2013. Mineral chemistry of hydrothermal biotite from the Kahang porphyry copper deposit (NE Isfahan), Central Province of Iran[J]. Ore Geology Reviews, 54: 214~232.

Anderson J L, Barth A P, Wooden J L, et al. 2008. Thermometers and thermobarometers in granitic systems[J]. Reviews in Mineralogy and Geochemistry, 69(1): 121~142.

Ayati F, Yavuz F, Noghreyan M, et al. 2008. Chemical characteristics and composition of hydrothermal biotite from the Dalli porphyry copper prospect, Arak, central province of Iran[J]. Mineralogy and Petrology, 94: 107~122.

Boomeri M, Nakashima K and Lentz D R. 2009. The Miduk porphyry Cu deposit, Kerman, Iran: A geochemical analysis of the potassic zone including halogen element systematics related to Cu mineralization processes[J] Journal of Geochemical Exploration, 103: 17~29.

Boomeri M, Nakashima K and Lentz D R. 2010. The Sarcheshmeh porphyry copper deposit, Kerman, Iran: A mineralogical analysis of the igneous rocks and alteration zones including halogen element systematics related to Cu mineralization processes[J]. Ore Geology Reviews, 38: 367~381.

Dada O A. 2013. Application of amphibole chemistry in determining the petrogenesis of hornblende-biotite granites from Toro complex, north central, Nigeria[J]. Continental Journal of Earth Sciences, 8: 1~11.

David R W and Hans P E. 1965. Stability of biotite: Experiment, theory, and application[J]. American Mineralogist, 50(9): 1 228~1 272.

Ding Xiaoshi. 1988. Study of typomorphic characteristica of micas from granitoids in central-southern Xizang and their geological significance[A]. Bulletin of the Institute of Mineral Deposits Chinese Academy of Geological Sciences[C]. (21): 33~50(in Chinese).

Duan J L, Tang X, Mason R, et al. 2014. Zircon U-Pb age and deformation characteristics of the Jiama porphyry copper deposit, Tibet: Implications for relationships between mineralization, structure and alteration[J]. Resoure Geology, 64: 316~331.

Foster M D. 1960. Interpretation of the composition of trioctahedral micas[J]. United States Geological Survey Professional Paper, 354-B: 11~49.

Fu Jinbao. 1981. Chemical composition of biotite in porphyry copper deposits[J]. Geology and Prospecting, (9): 16~19(in Chinese).

Henry D J. 2005. The Ti-saturation surface for low-to-medium pressure metapelitic biotites: Implications for geothermometry and Ti-substitution mechanisms[J]. American Mineralogist, 90: 316~328.

Hou Zengqian, Yang Zhiming, Wang Rui, et al. 2020. Further discussion on porphyry Cu-Mo-Au deposit formation in Chinese mainland[J]. Earth Science Frontiers, 27(2): 20~44(in Chinese with English abstract).

Jiang Changyi and An Sanyuan. 1984. On chemical characteristics of calcic amphiboles from igneous rocks and their petrogenesis significance[J]. J. Mineral Petrol. , (3): 1~8(in Chinese with English abstract).

Kumar S and Pathak M. 2010. Mineralogy and geochemistry of biotites from Proterozoic granitiods of western Arunachal Himalaya: Evidence of bimodal granitogeny and tectonic affinity[J]. Journal of Geological Society of India, 75(5): 715~730.

Leake B E, Woolley A R, Arps C E S, et al. 1997. Nomenclature of amphiboles: Report of the subcommittee on amphiboles of the international mineralogical association, commission on new minerals and mineral names[J]. The Canadian Mineralogist, 35: 219~246.

Lin Bin, Tang Juxing, Tang Pan, et al. 2019. Polycentric complex mineralization model of porphyry system: A case study of Jiama superlarge deposit in Tibet[J]. Mineral Deposits, 38(6): 1 204~1 222(in Chinese with English abstract).

Lin Wenwei and Peng Lijuan. 1994. The estimation of Fe3+ and Fe2+ contents in amphibole and biotite from EMPA data[J]. Journal of Changchun University of Earth Sciences, 24: 155~162(in Chinese with English abstract).

Lu Y J, Locuks R R, Fiorentini M L, et al. 2015. Fluid flux melting generated postcollisional high Sr/Y copper ore-forming water-rich magmas in Tibet[J]. Geology, 43(7): 583~586.

Luan Y, Song X Y, Chen L M, et al. 2014. Key factors controlling the accumulation of the Fe-Ti oxides in the Hongge layered intrusion in the Emeishan Large Igneous Province, SW China[J]. Ore Geology Review, 57: 518~538.

Lü Zhicheng, Li Henian, Liu Congqiang, et al. 2000. Mineralogical and geochemical charateristics of biotite in granite in south-middle section of the great Xing'an mountains and its genetic significance[J]. J. Mineral. Petrol. , 20(3): 1~8(in Chinese with English abstract).

Mengason M J, Candela P A and Piccoli P M. 2011. Molybdenum, tungsten and manganese partitioning in the system pyrrhotite-Fe-S-O melt-rhyolite melt: Impact of sulfide segregation on arc magma evolution[J]. Geochimica et Cosmochimica Acta, 75(22): 7 018~7 030.

Nandedkar R H, Ulmer P and Müntener O. 2014. Fractional crystallization of primitive, hydrous arc magmas: An experimental study at 0.7 GPa[J]. Contributions to Mineralogy and Petrology, 167(6): 1 015.

Parsapoor A, Khalili M, Tepley F, et al. 2015. Mineral chemistry and isotopic composition of magmatic, re-equilibrated and hydrothermal biotites from Darreh-Zar porphyry copper deposit, Kerman (Southeast of Iran)[J]. Ore Geology Reviews, 66: 200~218.

Qin Zhipeng. 2010. The Diagenesis and Mineralization of Quasi-adakite in the Jiama Copper Polymetallic Deposit[D]. Chengdu University of Technology(in Chinese).

Qin Zhipeng. 2013. Genetic Model of the Jiama Copper-Polymetallic Ore Deposits, Tibet[D]. Chengdu University of Technology(in Chinese).

Richards J. 2003. Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[J]. Economic Geology, 98(8): 1 515~1 533.

Ridolfi F, Pierini M, Renzulli A, et al. 2008. The magmatic feeding system of EI Reventador volvano (Sub-Andean zone, Ecuador) constrained by texture, mineralogy and thermobarometry of the 2002 erupted products [J]. J. Volcanol. Geotherm. Res. , 176(1): 94~106.

Ridolfi F and Renzulli A. 2012. Calcic hornblendes in calc-alkaline and alkaline magmas: Thermobarometric and chemometric empirical equations valid up to 1 130℃ and 2. 2 GPa[J]. Contributions to Mineralogy and Petrology, 163: 877~895.

Ridolfi F, Renzulli A and Puerini M. 2010. Stability and chemical equilibrium of hornblende in calc-alkaline magmas: An overview, new thermobarometric formulations and application to subduction-related volcanoes[J]. Contributions to Mineralogy and Petrology, 160(1): 45~66.

Ridolfi F, Zanetti A, Renzulli A, et al. 2018. AMFORM, a new mass-based model for the calculation of the unit formula of hornblendes from electron microprobe analyses [J]. American Mineralogist, 103(7): 1 112~1 125.

Shen P, Hattori Keiko, Pan H D, et al. 2015. Oxidation condition and metal fertility of granitic magmas: Zircon trace-element data from porphyry Cu deposits in the central Asian orogenic belt[J]. Economic Geology, 110: 1 861~1 878.

Siahcheshm K, Calagari A A, Abedini A, et al. 2012. Halogen signatures of biotites from the Maher-Abad porphyry copper deposit, Iran: Characterization of volatiles in syn- to post-magmatic hydrothermal fluids[J]. International Geology Review, 54: 1 353~1 368.

Stone D. 2000. Temperature and pressure variations in suites of Archean felsic plutonic rocks, Berens River area, northwest Superior Province, Ontario, Canada[J]. The Canadian Mineralogist, 38(2): 455~470.

Sun W D, Huang R F, Li H, et al. 2015. Porphyry deposits and oxidized magmas[J]. Ore Geology Reviews, 65: 97~131.

Tang Juxing, Deng Shilin, Zheng Wenbao, et al. 2011. An exploration model for Jiama copper polymetallic deposit in Maizhokunggar County, Tibet[J]. Mineral Deposits, 30: 179~196(in Chinese with English abstract).

Tang Juxing, Wang Denghong, Wang Xiongwu, et al. 2010. Geological features and metallogenic model of the Jiama copper-polymetallic deposit in Tibet[J]. Acta Geoscientica Sinica, 31: 495~506(in Chinese with English abstract).

Tang Juxing and Wang Qin. 2019. Advantages of copper resources and prospects for their exploitation and utilization inTibet[J]. Strategic Study of CAE, 21(1): 140~147(in Chinese with English abstract).

Tang Juxing, Zheng Wenbao, Chen Yuchuan, et al. 2013. Prospecting breakthrough of the deep porphyry ore body and its significance in Jiama copper polymetallic deposit, Tibet, China[J]. Journal of Jilin University(Earth Science Edition), 43: 1 100~1 110 (in Chinese with English abstract).

Tang Pan. 2018. Mineralogical Characteristics of Biotites from the Porphyry Copper-Polymetallic Deposits in Gangdese Metallogenic Belt, Tibet: Implication for Metallogenetic Environment[D]. Chengdu University of Technology (in Chinese).

Tang Pan, Chen Yuchuan, Tang Juxing, et al. 2016b. Characteristics and geological significance of biotites in Jiama porphyry deposit system, Tibet [J]. Mineral Deposits, 35(4): 846~866.

Tang P, Cheng Y C, Tang J X, et al. 2019a. Advances in research of mineral chemistry of magmatic and hydrothermal biotites[J]. Acta Geologica Sinica (English Edition), 93(6): 1 947~1 966.

Tang Pan, Tang Juxing, Leng Qiufeng, et al. 2016a. S, Pb isotope composition and source tracing of ore-forming materials in the Lunlang lead-zinc deposit, Tibet[J]. Acta Petrologica et Mineralogica, 35(6): 1 045~1 054(in Chinese with English abstract).

Tang P, Tang J X, Lin B, et al. 2019b. Mineral chemistry of magmatic and hydrothermal biotites from the Bangpu porphyry Mo (Cu) deposit, Tibet[J]. Ore Geology Reviews, 115: 103~122.

Tang Pan, Tang Juxing, Zheng Wenbao, et al. 2017a. Is Tongshan orebody in Jiama copper- polymetallic deposit manto-type ore?[J]. Acta Geoscientica Sinica, 38(5): 829~838(in Chinese with English abstract).

Tang Pan, Tang Juxing, Zheng Wenbao, et al. 2017b. Mineral chemistry of hydrothermal biotites from the Lakang’e porphyry Cu-Mo deposit, Tibet[J]. Earth Science Frontiers, 24: 265~282(in Chinese with English abstract).

Wang Weiping, Tang Juxing and Ying Lijuan. 2012. Mineral chemical characteristics of biotites from hornfels in the Jiama(Gyama) polymetallic copper deposit of Tibet and their geological significance[J]. Acta Geoscientica Sinica, 33(4): 444~458(in Chinese with English abstract).

Wang Yiyun, Zheng Wenbao, Chen Yuchuan, et al. 2017. Descussion on the mechanism of separation of copper and molybdenum in Jiama porphyry deposit system, Tibet[J]. Acta Petrologica Sinica, 33(2): 495~514 (in Chinese with English abstract).

Wang R, Richards J P, Hou Z Q, et al. 2014. Increased magmatic water content: The key to Oligo-Miocene porphyry Cu-Mo±Au formation in the eastern Gangdese belt, Tibet[J]. Economic Geologists, 109(5): 131~139.

Webster J D. 2004. The exsolution of magmatic hydrosaline chloride liquids[J]. Chemical Geology, 210: 33~48.

Whalen J B and Chappell B W. 1988. Opaque mineralogy and mafic mineral chemistry of I- and S-type granites of the Lachlan fold belt, southeast Australia[J]. American Mineralogist, 73(3~4): 281~296.

Wones D R and Eugster H P. 1965. Stability of biotite-experiment theory and application[J]. American Mineralogist, 50(9): 1 228.

Wu Huanhuan, Wang Tao, Zhang Zhaocong, et al. 2019. Chemical characteristics of amphibole and biotite from the Boziguo’er alkaline granitic pluton in Baicheng County, Xinjiang, and their implications for petrogenesis and mineralization[J]. Acta Petrologica et Mineralogica, 38(2): 173~190(in Chinese with English abstract).

Xiang Kun, Xue Chuandong, Xie Zhipeng, et al. 2019. Petrogenesis of the late Yanshanian Laba granite in northwestern Yunnan Province and its metallogenic implications: Evidence from mineral chemistry of biotites and amphiboles[J]. Acta Petrologica et Mineralogica, 38(1): 34~46(in Chinese with English abstract).

Xiao Hongtian, Xie Fuwei, Lang Xinghai, et al. 2020. Hydrothermal biotite characteristics and geological significance of No. Ⅰ and No. Ⅱ orebodies of the Xiongcun porphyry copper (gold) deposit in Tibet[J]. Acta Petrologica et Mineralogica, (4): 469~480(in Chinese with English abstract).

Xie Yingwen and Zhang Yuquan. 1990. Peculiarities and genetic significance of hornblende from granite in the Hengduansan region [J]. Acta Mineralogica Sinica, 10(1): 35~45(in Chinese).

Xu Keqin and Tu Guangchi. 1986. Relationship between Granitic Rocks and Mineralization[M]. Nanjing: Science and Technology of Jiangsu Press, 657(in Chinese).

Xu Keqin, Sun Nai, Wang Dezi, et al. 1984. Genesis of Huanan Granitic Rocks and Mineralization[M]. Nanjing: Science and Technology of Jiangsu Press, 1~20(in Chinese).

Ying Lijuan, Tang Juxing, Wang Denghong, et al. 2011. Zircon SHRIMP U-Pb dating of porphyry vein from the Jiama copper polymetallic deposit in Tibet and its significance[J]. Acta Petrologica Sinica, 27(7): 2 095~2 102(in Chinese with English abstract).

Zhang Dongyang, Zhang Zhaocong, Ai Yu, et al. 2009. Mineralogy of ore-bearing porphyries in Lailisigao’er area of the West Tianshan Mountain and its implications for petrogenesis and mineralization[J]. Acta Petrologica et Mineralogica, 28(1): 3~16(in Chinese with English abstract).

Zhang Juquan, Li Shengrong and Lu Jin. 2018. Calculation of oxygen fugacity for intermediate-acidic intrusive rocks[J]. Acta Mineralogica Sinica, 38(1): 1~14(in Chinese with English abstract).

Zhang Zebin, Tang Juxing, Tang Pan, et al. 2019. The origin of the mafic microgranular enclaves from Jiama porphyry Cu polymetallic deposit, Tibet: Implications for magma mixing/mingling and mineralization[J]. Acta Petrologica Sinica, 35(3): 934~952(in Chinese with English abstract).

Zhao Yiming, Lin Wenwei, Bi Xianzhong, et al. 2012. Skarn Deposits in China[M]. Geological Publishing House, 52~56(in Chinese).

Zheng Wenbao, Chen Yuchuan, Song Xin, et al. 2010. Element distribution and geological significance in the Jiama copper polymetallic deposit, Tibet[J]. Mineral Deposits, 29(5): 775~784(in Chinese with English abstract).

Zheng Wenbao, Tang Juxing, Wang Xiongwu, et al. 2012. Analysis on gold metallization in Jiama copper polymetallic deposit, Tibet [J]. Journal of Jilin University(Earth Science Edition), 42(s1): 181~196(in Chinese with English abstract).

Zheng W B, Tang J X, Zhong K H, et al. 2016. Geology of the Jiama porphyry copper-polymetallic system, Lhasa Region, China[J]. Ore Geology Reviews, 74: 151~169.

Zhong Kanghui, Li Lei, Zhou Huiwen, et al. 2012. Features of Jiama(Gyama)-Kajunguo thrust-gliding nappe tectonic[J]. Acta Geoscientica Sinica, 33(4): 411~423(in Chinese with English abstract).

Zhou Zuoxia. 1986. The origin of intrusive mass in Fengshandong, Hubei province[J]. Acta Petrotogica Sinica, 2(1): 59~70(in Chinese with English abstract).

Zhou Yun, Wang Xiongwu, Tang Juxing, et al. 2011a. Origin and evolution of ore-forming fluids from Jiama copper polymetallic deposit in Tibet [J]. Mineral Deposits, 30(2): 231~248(in Chinese with English abstract).

Zhou Yun, Wang Xiongwu, Tang Juxing, et al. 2011b. Composition of single melt inclusion in quartz phenocryst in the Jiama Cu-polymetallic Deposit, Tibet[J]. Journal of Chengdu University of Technology, 38(1): 92~102(in Chinese with English abstract).

Zou Bin, Lin Bin, Zheng Wenbao, et al. 2019. The characteristics of alteration and mineralization and geochronology of ore-bearing porphyry in south pit of Jiama copper-polymetallic deposit, Tibet[J]. Acta Petrologica Sinica, 35(3): 953~967(in Chinese with English abstract).

附中文参考文献

丁孝石. 1988. 西藏中南部各类花岗岩中黑云母标型特征及其地质意义[A]. 中国地质科学院矿床地质研究所文集[C], (21): 33~50.

侯增谦, 杨志明, 王 瑞, 等. 2020. 再论中国大陆斑岩Cu-Mo-Au矿床成矿作用 [J]. 地学前缘, 27(2): 20~44.

傅金宝. 1981. 斑岩铜矿中黑云母的化学组成特征[J]. 地质与勘探, 9(1): 16~19.

姜常义, 安三元. 1984. 论火成岩中钙质角闪石的化学组成特征及其岩石学意义[J]. 矿物岩石, (3): 1~8.

林 彬, 唐菊兴, 唐 攀, 等. 2019. 斑岩成矿系统多中心复合成矿作用模型——以西藏甲玛超大型矿床为例[J]. 矿床地质, 38(6): 1 204~1 222.

林文蔚, 彭丽君. 1994. 由电子探针分析数据估算角闪石、黑云母中的Fe3+ 、Fe2+[J]. 长春地质学院院报, 24(2): 155~162.

吕志成, 段国正, 郝立波, 等. 2003. 大兴安岭中南段燕山期两类不同成矿花岗岩类角闪石的化学成分及其成岩成矿意义[J]. 矿物岩石, (01): 5~10.

秦志鹏. 2010. 西藏甲玛铜多金属矿床似埃达克岩的成岩成矿作用[D]. 成都: 成都理工大学.

秦志鹏. 2013. 西藏甲玛铜多金属矿床成因模式[D]. 成都: 成都理工大学.

唐菊兴, 邓世林, 郑文宝, 等. 2011. 西藏墨竹工卡县甲玛铜多金属矿床勘查模型[J]. 矿床地质, 30(2): 179~196.

唐菊兴, 王登红, 汪雄武, 等. 2010. 西藏甲玛铜多金属矿矿床地质特征及其矿床模型[J]. 地球学报, 31(4): 495~506.

唐菊兴, 王 勤. 2019. 西藏铜矿资源优势及开发利用展望[J]. 中国工程科学: 21(01): 140~147.

唐菊兴, 郑文宝, 陈毓川, 等. 2013. 西藏甲玛铜多金属矿床深部斑岩矿体找矿突破及其意义[J]. 吉林大学学报(地球科学版), 43(4): 1 100~1 110.

唐 攀. 2018. 西藏冈底斯成矿带斑岩铜多金属矿床黑云母矿物学特征——对成矿环境的指示[D]. 成都: 成都理工大学.

唐 攀, 陈毓川, 唐菊兴, 等. 2016b. 西藏甲玛斑岩矿床系统黑云母特征及其地质意义[J]. 矿床地质, 35(4): 846~866.

唐 攀, 唐菊兴, 冷秋锋, 等. 2016a. 西藏轮郎铅锌矿床S、Pb同位素组成及对成矿物质来源的示踪[J]. 岩石矿物学杂志, 35(6): 1 045~1 054.

唐 攀, 唐菊兴, 郑文宝, 等. 2017a. 西藏甲玛铜多金属矿床铜山矿体为manto型矿体?[J] 地球学报, 38(5): 829~838.

唐 攀, 唐菊兴, 郑文宝, 等. 2017b. 西藏拉抗俄斑岩铜钼矿床黑云母矿物化学特征[J]. 地学前缘, 24(5): 265~282.

王崴平, 唐菊兴, 应立娟. 2012. 甲玛铜多金属矿床角岩中黑云母矿物化学特征及其地质意义[J]. 地球学报, 33(4): 444~458.

王艺云, 郑文宝, 陈毓川, 等. 2017. 西藏甲玛斑岩成矿系统铜钼元素分离机制探讨[J]. 岩石学报, 33, 495~514.

吴欢欢, 王 涛, 张招崇, 等. 2019. 新疆拜城县波孜果尔碱性花岗岩体中角闪石与黑云母地球化学特征及其对成岩成矿的记录[J]. 岩石矿物学杂志, 38(2): 173~190.

谢应雯, 张玉泉. 1990. 横断山区花岗岩类中角闪石的标型特征及其成因意义[J]. 矿物学报, (01): 35~45.

向 坤, 薛传东, 谢志鹏, 等. 2019. 滇西北拉巴燕山晚期花岗岩岩石成因及其成矿指示——黑云母和角闪石矿物化学证据[J]. 岩石矿物学杂志, 38(1): 34~46.

肖鸿天, 谢富伟, 郎兴海, 等. 2020. 西藏雄村斑岩型铜(金)矿床Ⅰ、Ⅱ号矿体热液黑云母特征及地质意义[J]. 岩石矿物学杂志, 39(4): 469~480.

徐克勤, 孙 鼐, 王德滋, 等. 1984. 华南花岗岩成因与成矿[C]. 江苏科学技术出版社, 1~20.

徐克勤, 涂光炽. 1986. 花岗岩地质和成矿关系[M]. 江苏科学技术出版社, 657.

应立娟, 唐菊兴, 王登红, 等. 2011. 西藏甲玛超大型铜矿区斑岩脉成岩时代及其与成矿的关系[J]. 岩石学报, 27(7): 2 095~2 102.

张东阳, 张招崇, 艾 羽, 等. 2009. 西天山莱历斯高尔一带铜(钼)矿成矿斑岩体矿物学特征及其成岩成矿意义[J]. 岩石矿物学杂志, 28(1): 3~16.

张聚全, 李胜荣, 卢 静. 2018. 中酸性侵入岩的氧逸度计算[J]. 矿物学报, 38(1): 1~14.

张泽斌, 唐菊兴, 唐 攀, 等. 2019. 西藏甲玛铜多金属矿床暗色包体岩石成因: 对岩浆混合和成矿的启示[J]. 岩石学报, 35(3): 934~952.

赵一鸣, 林文蔚, 毕承忠, 等. 2012. 中国矽卡岩矿床[M]. 地质出版社, 52~56.

郑文宝, 陈毓川, 宋鑫, 等. 2010. 西藏甲玛铜多金属矿元素分布规律及地质意义[J]. 矿床地质, 29(5): 775~784.

郑文宝, 唐菊兴, 汪雄武, 等. 2012. 西藏甲玛铜多金属矿床金矿地质特征及成矿作用[J]. 吉林大学学报(地球科学版), 42(增刊1): 181~196.

钟康惠, 李 磊, 周慧文, 等. 2012. 西藏甲玛-卡军果推-滑覆构造系特征[J]. 地球学报, 33(4): 411~423.

周 云, 汪雄武, 唐菊兴, 等. 2011a. 西藏甲玛铜多金属矿床成矿流体来源及演化[J]. 矿床地质, 30(2): 231~248.

周 云, 汪雄武, 唐菊兴, 等. 2011b. 西藏甲玛铜多金属矿含矿斑岩石英斑晶单个熔融包裹体的成分研究[J]. 成都理工大学学报: 自然科学版, 38(1): 92~102.

周作侠. 1986. 湖北丰山洞岩体成因探讨[J]. 岩石学报. 2(1): 59~70.

邹 兵, 林 彬, 郑文宝, 等. 2019. 西藏甲玛矿床南坑矿段蚀变、矿化及含矿斑岩年代学[J]. 岩石学报, 35(3): 953~967.

Mineral chemistry of biotite and hornblende of ore-bearing porphyry from the Jiama porphyry copper-polymetallic deposit

ZHANG Zhong-kun1, CHEN Guo-liang1, YANG Zheng-kun1, TANG Pan2, GAO Fu-tai1, JIAO Hai-jun1, WANG Zhi-chao3, QI Jing3 and WU Chun-neng4

(1. Huatailong Mining Development Co. Ltd., Lhasa 850200, China; 2. Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 611756, China; 3. School of Earth Science and Resources, China University of Geosciences(Beijing), Beijing 100083, China; 4. School of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China)

Abstract: The Jiama superlarge copper-polymetallic deposit is located in the eastern part of the Gangdise metallogenic belt, and mainly includes four types of orebodies: skarn orebody, porphyry orebody, hornfels orebody and independent gold orebody. There are extensive magmatic biotites in the intermediate acid intrusions of the deposit, and hornblende is more common in some intrusions. On the basis of comprehensive geological survey in the mining area and detailed drilling core cataloging, the authors studied mineralogy and mineral chemistry of magmatic biotite in ore-bearing monzogranite porphyry and ore-bearing granodiorite porphyry as well as hornblende in ore-bearing granodiorite porphyry so as to reveal its petrogenic and metallogenic significance. The results show that the magmatic biotite in monzogranite porphyry and granodiorite porphyry is Mg-biotite, which is characterized by higher MgO, TiO2, Al2O3, K2O contents, and lower SiO2, Na2O content. Compared with granodiorite porphyry, magmatic biotite in monzonitic granite porphyry has lower content of TiO2, FeOT, MgO, MnO, Na2O, BaO, and higher content of Al2O3, SiO2. Hornblende in granodiorite porphyry belongs to actinolite, which is characterized by higher SiO2, MgO and CaO content, and lower Al2O3, TiO2, Na2O and K2O content. Biotite and hornblende thermometers show that the crystallization temperature of biotite in ore-bearing monzogranite porphyry is 740.1~783.8℃, with an average of 762.4℃, that of biotite in ore-bearing granodiorite porphyry is 750.3~766.9℃, with an average of 757.2℃, and that of hornblende in ore-bearing granodiorite porphyry is 654.1~698.9℃, with an average of 680.3℃. The mineral chemical characteristics of biotite and hornblende indicate that monzogranite porphyry and granodiorite porphyry are calc-alkaline series and I-type granite in the orogenic belt, which has the characteristics of crust-mantle mixed source. Monzogranite porphyry and granodiorite porphyry had higher oxygen fugacity (above NNO) and formed water-rich magmas, which was beneficial for the entry of copper, molybdenum and other ore-forming materials into ore-forming fluid.

Key words: hornblende; biotite; mineral chemistry; Jiama; Tibet

中图分类号: P578.955P578.959P618.41

文献标识码:A

文章编号:1000-6524(2020)06-0685-18

收稿日期: 2020-07-02; 接受日期:2020-09-06; 编辑:郝艳丽

基金项目: 国家重点研发计划-深地专项(2018YFC0604101); 中国地质科学院基本科研业务费专项经费项目(SYSCR2019-02); 西藏自治区科技计划项目(XZ201901-GB-24); 国家自然科学基金项目(41902097); 中国地质调查局项目(DD20190167)

作者简介: 张忠坤(1967- ), 男, 高级工程师, 主要从事固体矿产勘查和开发, E-mail: zzk19671004@163.com;

通讯作者:唐 攀(1989- ), 男, 博士后, 主要从事青藏高原矿产勘查和综合研究, E-mail: tangpan@163.com。

Fund support:National Key Research and Development Program of China (2018YFC0604101); Basic Research Fund of the Chinese Academy of Geological Sciences (SYSCR2019-02); Sciences and Technical Plan from Tibet (XZ201901-GB-24); National Natural Science Foundation of China (41902097); China Geological Survey Project (DD20190167)