西藏林子宗群火山巖中首次發現低硫化型淺成低溫熱液型礦床
——以斯弄多銀多金屬礦為例

唐菊興, 丁 帥, 孟 展, 胡古月, 高一鳴, 謝富偉, 李 壯,袁 梅, 楊宗耀, 陳國榮, 李于海, 楊洪鈺, 付燕剛

1)中國地質科學院礦產資源研究所, 國土資源部成礦作用與資源評價重點實驗室, 北京 100037;

2)成都理工大學地球科學學院, 四川成都 610059;

3)西藏中瑞礦業發展有限責任公司, 西藏拉薩 850000; 4)中國地質大學(北京), 北京 100083

西藏林子宗群火山巖中首次發現低硫化型淺成低溫熱液型礦床
——以斯弄多銀多金屬礦為例

唐菊興1), 丁 帥2), 孟 展2), 胡古月1), 高一鳴1), 謝富偉2), 李 壯2),袁 梅2), 楊宗耀2), 陳國榮3), 李于海3), 楊洪鈺3), 付燕剛4)

1)中國地質科學院礦產資源研究所, 國土資源部成礦作用與資源評價重點實驗室, 北京 100037;

2)成都理工大學地球科學學院, 四川成都 610059;

3)西藏中瑞礦業發展有限責任公司, 西藏拉薩 850000; 4)中國地質大學(北京), 北京 100083

西藏岡底斯成礦帶分布著大面積古近紀(70–40 Ma)林子宗群火山巖。但如此強烈的火山-巖漿作用,與安第斯成礦帶相比(如馬力昆帶(Franja de Maricunga)、印地—帕斯瓜帶(Franja El Indio-Pascua)), 除了碰撞伸展階段形成的驅龍、甲瑪等斑巖-矽卡巖型銅多金屬礦床外(23–13 Ma), “缺位”資源規模大、經濟價值高的淺成低溫熱液型礦床成礦亞系列。該類礦床是剝蝕了, 還是沒有發現？本文在前人工作基礎上, 通過詳細的地質勘探、地質填圖、地質編錄、鏡下鑒定、能譜和電子探針分析, 在南木林盆地斯弄多地區林子宗群陸相火山巖中識別出低硫化淺成低溫熱液型銀鉛鋅(銦鎘金)礦床。礦體由產于流紋斑巖中的隱爆角礫巖型銀鉛鋅礦體、火山機構旁側的熱液脈型銀鉛鋅礦體及斷裂上盤的銀(鉛鋅)礦體組成, 目前控制Pb+Zn資源量超過30萬噸(331+332為主)@Pb+Zn＞5％, Ag資源量超過400噸@Ag＞50 g/t。主要金屬礦物為方鉛礦、閃鋅礦、輝銀礦、硫砷銅銀礦、黃鐵礦, 微量黃銅礦, 主要蝕變組合為: 石英-玉髓-碧玉, 重晶石-螢石, 冰長石-伊利石-絹云母, 菱鐵礦-菱錳礦; 礦石構造以脈狀、角礫狀、網脈狀、條帶狀、層紋狀、皮殼狀、塊狀、浸染狀等, 發育結晶作用和交代作用形成的礦石結構; 近地表發育古熱泉噴口, 堆積條帶狀、層紋狀硅質沉積物。綜合上述地質信息, 確定該礦床為典型低硫化淺成低溫熱液型銀多金屬礦床。這一重要礦床類型的發現和確定在岡底斯成礦帶乃至西藏特提斯成礦省尚屬首例, 對岡底斯成礦帶廣泛發育形成于70～40 Ma的林子宗群火山巖地區區域找礦具有積極和重要的指導意義, 其重要性不容低估。

斯弄多; 林子宗群火山巖; 冰長石-絹云母-伊利石; 低硫化型; 淺成低溫熱液銀多金屬; 岡底斯

“淺成低溫熱液”這一術語最初由Lindgren (1922)對熱液礦床按其形成的溫度和深度進行分類研究時首次提出。其后, 許多研究者不斷對淺成低溫熱液型礦床含義及分類進行著補充和完善, 目前定義為含礦熱液上升至淺地表(＜2 km)、在中低壓(＜100 Pa)、中低溫度(200～300℃)條件下形成的一類礦床(Lindgren, 1922, 1933; Hendenquist, 1987; White and Hendenquist, 1990; Hendenquist et al., 2000; Corbett, 2002; Simmons et al., 2005)。并根據流體中硫的氧化還原態與蝕變礦物組合劃分為高硫化(明礬石-高嶺石型)和低硫化(冰長石-絹云母型)兩種端元類型(Hendenquist, 1987; Heald et al., 1987; Einaudi et al., 2003; Sillitoe and Hedenquist, 2003)。同時,隨著全球范圍內大量淺成低溫熱液型礦床相繼被發現, 這類礦床逐漸成為全球金、銀、銅、鉛、鋅等有色資源重要礦床類型之一(Corbett, 2002; 江思宏等, 2004; Sidorov et al., 2015; Páez et al., 2016), 地質學家們逐漸認識到這類礦床主要產于板塊俯沖帶邊緣的島弧、陸緣弧中(Hendenquist et al., 2000; Corbett, 2002; Richards, 2013), 與同期陸相火山-次火山活動在時空上有著密切聯系, 并強調火山作用對成礦的貢獻(Sidorov et al., 2015; Nadeau et al., 2016)。

西藏岡底斯帶發育的多條不同時期、線性分布的火山-巖漿巖帶是形成大-超大型礦床的有利條件,現已發現多個具有重要經濟價值的斑巖-矽卡巖型銅多金屬礦(如: 甲瑪、驅龍、雄村、幫浦等)、矽卡巖型鉛鋅礦(龍瑪拉、洞中拉—洞中松多、亞貴拉等)及熱液脈型銀鉛鋅礦床, 使得該區成為我國一條重要銅多金屬成礦帶(Hou et al., 2009; 郎興海等, 2012; 唐菊興等, 2012, 2014a, b; Tang et al., 2015; Zheng et al., 2016)。作為岡底斯構造-巖漿-成礦帶中規模最大的林子宗群火山巖, 其東西展布大于1 200 km, 分布范圍占岡底斯巖漿帶面積的一半以上(圖1a)(Mo et al., 2008), 與岡底斯大巖基一起構成岡底斯帶最重要的巖漿巖組合, 代表著白堊紀晚期—早新生代(70—40 Ma)青藏高原南部的一次大規模的構造巖漿事件(Ding et al., 2003, 2005; 侯增謙等, 2006)。然而, 如此強烈的火山-巖漿活動是否伴有重要的成礦作用？與安第斯成礦帶相比(如馬力昆帶(La Franja de Maricunga)、印地—帕斯瓜帶(Franja El Indio-Pascua)), 是否形成與之類似的淺成低溫熱液型貴金屬礦床？盡管近年來南木林盆地相繼發現了諸如納如松多、則學等多個中-大型礦床,但產于林子宗群中的礦床至今尚未引起足夠的重視。賦存于林子宗群火山巖中的斯弄多銀多金屬礦床的發現, 為深入研究及剖析該套火山巖的形成與成礦關系提供了良好的契機。為此, 本文以新發現的斯弄多銀多金屬礦為研究對象, 通過詳細的地質勘探、地質填圖、地質編錄、鏡下鑒定、能譜和電子探針分析, 確定礦床類型, 對岡底斯成礦帶廣泛發育林子宗群火山巖地區的區域找礦具有積極和重要的指導意義。

圖1 西藏地區構造分區圖(a) (根據Hou et al., 2004修改)和岡底斯北帶區域地質及礦床分布圖(b) (根據Zheng et al., 2016修改)Fig. 1 Sketch tectonic map (a) (modified after Hou et al., 2004) and simplified regional geological map of northeastern Gangdese belt with ore deposits (b) (modified after Zheng et al., 2016)

圖2 斯弄多礦區地質圖(a)和斯弄多礦區剖面(b)Fig. 2 Geological map of the Sinongduo deposit (a) and section A-A’ of the Sinongduo deposit (b)

1 礦床地質

1.1 成礦地質背景

斯弄多礦區位于西藏自治區謝通門縣境內, 大地構造位置處于拉薩地體隆格爾—工布江達弧背斷隆帶上, 屬于岡底斯北緣Pb-Zn-Ag成礦帶中段(圖1a)。區域地層主要以火山-沉積建造為主, 研究區出露石炭—二疊系碳酸鹽-碎屑巖建造, 中生界(J3-K1)淺海相至海陸交互相碎屑巖、碳酸鹽巖建造, 新生界林子宗群(E1-2)陸相火山巖(圖1b), 該套火山巖自下而上劃分為典中組、年波組和帕那組, 成巖年齡集中在64.43～61.45 Ma、54.07 Ma、48.72～43.93 Ma(董國臣等, 2005), 其中典中組表現為弧火山巖特征, 年波組顯示為陸緣弧、碰撞和板內環境特征, 帕那組顯示為大陸碰撞、板內環境特征, 由南向北巖石堿度增高, 由東向西由偏基性過渡為偏酸性, 反應了由南向北大洋向大陸轉換, 巖漿源區具有不均一性的特征(Lee et al., 2009 Chen et al., 2014)。斯弄多礦區含礦圍巖為古新統典中組(E1d),其形成時代在60～62 Ma(丁帥等, 未刊數據), 巖性主要包括流紋斑巖、晶屑凝灰巖、火山角礫巖等(圖2a)。鄰區納如松多隱爆角礫巖型銀鉛鋅、則學熱液脈型鉛鋅銀礦則產于典中組火山巖中(紀現華等, 2012), 拉宗熱液脈型銀鉛鋅礦產于帕那組火山巖。區內發現多個火山機構, 具有典型火山角礫巖-流紋斑巖-凝灰巖巖相分帶, 火山機構旁側發育多條張性斷裂, 是熱液脈型礦體主要賦存空間。礦區巖漿巖主要為黑云母花崗斑巖, 呈巖脈、巖枝分布在13–15號勘探線附近(圖2a), 與典中組火山巖接觸帶多形成熱液隱爆角礫巖。

1.2 礦體特征

新發現銀鉛鋅礦體產于典中組火山巖中(前人認為是年波組火山巖), 2013—2014年西藏地質二隊開展了卓有成效的地質工作, 初步圈定了礦體, 但在礦床類型確定、礦體特征等方面研究程度較低。通過對鉆孔和探礦坑道詳細地質編錄, 根據賦礦圍巖及成礦元素共劃分出三種類型礦體, 即: 產于流紋斑巖中隱爆角礫巖型銀鉛鋅礦體、火山機構旁側受斷層破碎帶控制的熱液脈型鉛鋅銀礦體及斷裂上盤的獨立銀礦體。

隱爆角礫巖型礦體: 位于礦區西側, 近直立筒狀, 目前控制長60 m, 寬約30 m, 厚度約50 m(圖2b)。角礫成分主要為流紋斑巖及火山碎屑巖, 呈三角狀、板狀、橢圓狀及不規則狀, 大小0.5～10 cm之間, 占整個角礫巖體積約30％～50％, 膠結物主要為巖粉、石英、長石、絹云母、伊利石、菱鐵礦、菱錳礦及黃鐵礦、方鉛礦、閃鋅礦等硫化物(圖3a)。除了筒狀角礫巖型礦體以外, 還在脈狀礦體中發育大量脈狀、板狀隱爆角礫巖型礦石, 與塊狀、網脈狀礦石一同構成脈狀礦體。

脈狀礦體: 近南北向位于礦區中部, 是礦區規模最大、品位高的銀鉛鋅礦體, 主要產于火山機構旁側張性斷裂中, 呈板狀陡傾斜, 礦體走向長度超過300 m, 傾向延伸200 m, 厚度在2～30 m之間(圖2b)。方鉛礦、閃鋅礦等硫化物多呈塊狀、網脈狀、細脈狀集合體, 系含礦熱液沿構造裂隙充填交代作用形成(圖3b)。

獨立銀(鉛鋅)礦體: 分布在脈型礦體上盤, 多與紅色碧玉及含鐵錳碳酸鹽礦物密切共生(圖3c), Ag平均品位可達400～1 000 g/t。

截止目前, 斯弄多銀多金屬礦共探明Pb+Zn金屬量大于30萬噸, Ag金屬量超過400噸(331+332類別), 遠景規模可達大型。

1.3 礦石特征

礦區礦石呈典型熱液礦床的構造, 以塊狀、角礫狀、網脈狀為主, 局部發育脈狀-網脈狀、浸染狀礦石, 金屬礦物由方鉛礦、閃鋅礦、黃鐵礦、黃銅礦、輝銀礦、硫砷銅銀礦、黃鉀鐵礬、赤鐵礦和菱鐵礦、菱錳礦等組成(據丁帥等, 未刊電子探針數據)。其中方鉛礦多呈中細粒自形-半自形與黃鐵礦、閃鋅礦等礦物產出(圖3d); 閃鋅礦中多發育固溶體分離結構的黃銅礦(圖3e); 銀礦物主要為輝銀礦、硫砷銅銀礦, 除部分以類質同象形式產于方鉛礦中外(圖3f), 多數輝銀礦、硫砷銅銀礦等獨立銀礦物賦存于碧玉及鐵錳碳酸鹽裂隙中或呈粒間銀分布于早期硫化物晶隙間(圖3g, h), 與我國江西冷水坑及環太平洋地區淺成低溫熱液型Ag礦床極為類似(盧燃等, 2012; Chinchilla et al., 2016)。黃鐵礦呈浸染狀、脈狀, 在隱爆角礫巖中呈團斑狀, 粒徑以1～2 mm為主, 具有多階段形成特征, 早期黃鐵礦被方鉛礦、閃鋅礦等硫化物交代, 晚期黃鐵礦交代閃鋅礦。非金屬礦物可見石英、斜長石、絹云母、伊利石、玉髓、冰長石、方解石、重晶石, 螢石等(據丁帥等, 未刊電子探針數據)。根據鉆孔編錄、高光譜測量、光薄片鑒定和礦物能譜分析, 蝕變礦物組合有石英-玉髓-碧玉(圖3i, j), 重晶石-螢石, 冰長石-伊利石-絹云母(圖3k, l), 碳酸鹽礦物組合(包括鐵錳碳酸鹽巖(圖3m)及葉片狀方解石(圖3n))及表生硅華(圖3o)。其中石英-玉髓化分布在1號勘探線附近, 冰長石-伊利石-絹云母化疊加在石英-玉髓化之上, 鐵錳碳酸鹽分布在5–13號勘探線, 空間上與獨立銀礦物密切共生。

2 討論

2.1 低硫化淺成低溫熱液礦床的確定

Hendenquist(1987)依據流體中硫的氧化還原狀態將淺成低溫熱液型礦床劃分出高硫化和低硫化兩種類型(Hendenquist, 1987)。前者主要與安山質和流紋質巖漿活動有關, 由酸性、氧化的熱液流體形成(White and Hendenquist, 1990; Corbett, 2002; 張德全等, 2005), 以高含量的金銅硫化物及高價硫的明礬石+高嶺土等硫酸鹽礦物組合為主(Heald, 1987; Hendenquist, 1987; Sillitoe and Hedenquist, 2003; 唐菊興等, 2014b), 常見硅帽(由塊狀石英和多孔狀石英組合)(Corbett, 2002; 張元厚等, 2009; Elizabeth, 2012); 后者與堿性和偏堿性玄武質-流紋質巖漿活動有關, 由近中性、還原的熱流體形成(Corbett,2002; Taylor, 2007), 發育熱泉及隱爆角礫巖(Kouhestani et al., 2012), 常見刃片狀/葉片狀/板狀碳酸鹽及條帶狀、層紋狀、梳狀石英+玉髓+冰長石+絹云母+伊利石組合的蝕變, 以 金、銀、鉛、鋅礦化為主, 伴生銅、銻、硒等元素(Hendenquist, 1987; Simmons et al., 2000; Sillitoe and Hedenquist, 2003;Moncada et al., 2012)。

圖3 斯弄多礦區礦石、礦物及蝕變特征Fig. 3 The characteristics of ores, minerals and alterations in the Sinongduo deposita-角礫巖型礦體, 膠結物為黃鐵礦、方鉛礦及閃鋅礦等硫化物; b-熱液脈型礦體; c-高品位銀礦石; d-半自形粒狀方鉛礦; e-固溶體分離結構的閃鋅礦與黃銅礦; f-輝銀礦, 與方鉛礦共生體; g, h-碧玉等脈石礦物裂隙中的輝銀礦及硫砷銅銀礦; i-石英及玉髓脈; j-紅色碧玉,發育大量赤鐵礦; k-絹云母交代冰長石; l-鱗片狀伊利石; m-環狀鐵菱錳礦; n-葉片狀方解石; o-條帶狀熱泉噴口硅華; Py-黃鐵礦; Gn-方鉛礦; Sph-閃鋅礦; Ccp-黃銅礦; Arn-輝銀礦; Pe-硫砷銅銀礦; Hem-赤鐵礦; Q-石英; Cha-玉髓; Jas-碧玉; Ser-絹云母; Aul-冰長石; Ili-伊利石; Sd-菱錳礦; Cal-方解石; Si-硅質礦物a-breccia-type ores with the cement of pyrite, galena, sphalerite and other sulfides; b-hydrothermal vein-type orebody; c-high-grade silver ore; d-subhedral granular galena; e-exsolution texture of sphalerite and chalcopyrite; f-association of argentite and galena; g, h-argentite and proustite in the fissures of jasper and other gangue minerals; i-quartz and chalcedony veins; j-lots of hematites in red jasper; k-adularia replaced by sericite; l-flake illite; m-annular iron-rhodochrosite; n-bladed calcite; o-banded supergene geyserite; Py-pyrite; Gn-galena; Sph-sphalerite; Ccp-chalcopyrite; Arn-argentite; Pe-proustite; Hem-hematite; Q-quartz; Cha-chalcedony; Jas-jasper; Ser-sericite; Aul-adularia; Ili-illite; Sd-rhodochrosite; Cal-calcite; Si-siliceous minerals

斯弄多銀多金屬礦體賦存于林子宗群火山巖中, 包括產于流紋斑巖中隱爆角礫巖型銀鉛鋅礦體、火山機構旁側的熱液脈型鉛鋅銀礦體及斷裂上盤的獨立銀礦體。與世界上低硫化淺成低溫熱液型礦床有相似的礦化特征, 發育典型淺成低溫熱液系統中硅化-冰長石-碳酸鹽(鐵錳碳酸鹽+方解石)蝕變。硅化表現為石英+硅華+玉髓+碧玉等礦物組合(圖3i, j), 且表現出自上而下垂直分帶特征: 由淺部熱泉噴口附近的硅華→中部微細粒石英+玉髓脈→深部梳狀、脈狀石英。其中這些非晶質硅質礦物大多形成于相對高pH和中低溫(＜300℃)環境中(James, 1994), 反映了沸騰熱液在淺地表環境下快速冷卻沉淀條件(張元厚等, 2009)。冰長石形成溫度為180～320℃(Pirajno, 1992), 在近中性-堿性條件下大量鉀質蝕變而成(張元厚等, 2009), 后期多受絹云母等含水硅酸鹽礦物所交代(圖3k)。斯弄多礦區碳酸鹽化表現兩種形式: 鐵錳碳酸鹽和方解石(圖3m, n), 其中鐵錳碳酸鹽礦物在空間上與銀礦體相伴產出, 與我國江西冷水坑和浙東地區淺成低溫熱液型銀礦床極為相似(魏元柏和趙宇, 1996; 盧燃等, 2012)。一般認為這種鐵錳碳酸鹽形成于低溫(200℃左右), 中性環境中(pH在6.7左右)(Wei and Chen, 1993), 其形成加速了銀的沉淀速度, 促進了銀礦物(主要是自然銀)的析出(魏元柏和趙宇, 1996)。此外,礦區常見葉片狀方解石(圖3n), 這種方解石多因富揮發分流體快速沸騰, CO2較其他揮發分溶解度偏低, 而從液相中優先強烈分離進入氣水相, 促使方解石快速結晶并按扁平習性生長形成(Canet et al., 2011), 是低硫化淺成低溫熱液型礦床形成過程中存在流體沸騰的有利證據(Simon et al., 1999; Etoh et al., 2002)。以上這些礦物均反映了斯弄多礦區成礦流體具有淺成、低溫、中-還原性特征, 具有典型低硫化淺成低溫熱液型礦床成礦特征(Hendenquist et al., 2000; Corbett, 2002; Sillitoe and Hedenquist, 2003), 這在岡底斯成礦帶乃至西藏特提斯成礦省尚屬首例。

2.2 區域成礦前景

淺成低溫熱液型礦床的形成與深部巖漿作用形成的熱液體系密切相關, 其深部常發育斑巖型銅多金屬礦, 它們共同組成一個完整的火山-巖漿成礦系統(Sillitoe, 2010)。如在我國西藏多龍礦集區,鐵格隆南(榮那)礦段由淺部高硫化淺成低溫熱液與深部斑巖型銅(金、銀)型礦體組成, 這是我國目前已發現的規模最大的高硫型淺成低溫熱液-斑巖型礦床(唐菊興等, 2014b; 楊超等, 2014; 方向等, 2015;李光明等, 2015)。此外, 唐菊興等(2014a)按照斑巖礦床成礦系列的“缺位理論”, 提出雄村礦集區具有低硫化淺成低溫熱液型礦床找礦潛力, 并根據雄村外圍洞嘎金礦礦物組合認為其具有淺成低溫熱液型礦床特征。然而, 近年來在廣泛分布的陸相火山巖地區大量淺成低溫熱液型Au、Ag、Pb、Zn礦床(低硫型)相繼被發現, 地質學家們逐漸重視火山作用對成礦的貢獻, 同時強調火山作用中火山熱液體系是成礦關鍵因素(Sidorov et al., 2015; Nadeau et al., 2016)。

林子宗群火山巖是岡底斯成礦帶乃至青藏高原發育的最大規模的火山巖帶, 該套火山巖東西展布大于1 200 km, 分布范圍占岡底斯巖漿帶面積的一半以上(Mo et al., 2008), 代表著白堊紀晚期—早新生代(70～40 Ma)青藏高原南部的一次大規模的構造巖漿事件(Ding et al., 2003, 2005; 侯增謙等, 2006)。同時也是岡底斯Ag-Pb-Zn礦床重要賦礦層位, 包括納如松多、斯弄多、則學、扎扎龍等多個中-大型礦床均產于該套火山巖中。斯弄多銀多金屬礦是林子宗群火山巖中首次確定的低硫化淺成低溫熱液型礦床, 盡管這套火山巖對成礦作用影響尚未展開深入研究, 但其成礦環境可媲美安第斯成礦帶(如馬力昆成礦帶(La Franja de Maricunga)(John et al., 2001; Richards et al., 2013)、印地—帕斯瓜成礦帶(Franja El Indio-Pascua) (Deyella et al., 2005; Bissiga et al., 2015)等火山巖地區, 此外, 斯弄多礦區外圍還發現有多個熱液隱爆角礫巖筒及古熱泉噴口,是斑巖-淺成低溫熱液型銀、金礦床形成的有利條件,有望在該地區實現淺部未被剝蝕的獨立金礦體找礦突破。另一方面, 就整個岡底斯成礦帶上林子宗群火山巖而言, 其出露區域均與地球化學異常套合較好, Au、Ag等成礦元素均具有明顯的濃度分帶, 較高的峰值, 指示了林子宗群火山巖具有良好的找礦前景(李光明等, 2004; 譚鋼等, 2011), 是尋找斑巖-淺成低溫熱液型、隱爆角爍巖型、熱液脈型金、銀、鉛、鋅多金屬礦的有利地段。

3 結論及地質意義

1)斯弄多銀多金屬礦產于岡底斯成礦帶中段南木林火山盆地, 是在林子宗群陸相火山巖中新發現的中大型銀多金屬礦床, 由產于流紋斑巖中隱爆角礫巖型銀多金屬礦體、火山機構旁側的熱液脈型鉛鋅銀礦體及斷裂上盤的銀(鉛鋅)礦體組成。

2)礦石發育典型的條帶狀、層紋狀、皮殼狀、角礫狀、網脈狀礦石構造, 以石英-玉髓-碧玉-伊利石-絹云母-碳酸鹽等蝕變礦物組合為主, 顯示該礦床具有典型的低硫化淺成低溫熱液型礦床典型的礦石組構和蝕變礦物組合。

3)產于林子宗群火山巖中的低硫化淺成低溫熱液型礦床在岡底斯成礦帶上尚屬首次識別, 不僅豐富和完善了該區礦床類型, 同時對岡底斯成礦帶廣泛發育林子宗群火山巖地區的區域找礦具有積極和重要的指導意義, 對于1 200 km帶狀分布的林子宗群出露區的銀(金)多金屬礦找礦勘查其意義非同小可。

致謝:感謝西藏中瑞礦業發展有限責任公司黃若朝董事長、李祥總經理為筆者的野外工作和室內工作提供的資助。同時對編輯老師以及審稿專家為本文提出的寶貴意見, 在此深表謝意!

Acknowledgements:

This study was supported by China Geological Survey (No. 12120114068401), and Zhongrui Mining Co., Ltd. (No. XZZR-2015).

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The First Discovery of the Low Sulfidation Epithermal Deposit in Linzizong Volcanics, Tibet: A Case Study of the Sinongduo Ag Polymetallic Deposit

TANG Ju-xing1), DING Shuai2), MENG Zhan2), HU Gu-yue1), GAO Yi-ming1), XIE Fu-wei2), LI Zhuang2), YUAN Mei2), YANG Zong-yao2), CHEN Guo-rong3), LI Yu-hai3), YANG Hong-yu3), FU Yan-gang4)
1) MLR Key Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037; 2) College of Earth Sciences, Chengdu University of Technology, Chengdu, Sichuan 610059; 3) Zhongrui Mining Co., Ltd., Lhasa, Tibet 850000; 4) China University of Geosciences(Beijing), Beijing 100083

Sinongduo; Linzizong group volcanic rock; valencianite-illite-sericite; low sulfidation; epithermal Ag polymetallic deposit; Gangdise

P317.3; P618.4

A

10.3975/cagsb.2016.04.08

本文由中國地質調查局地質調查項目“西藏雄村-普桑果斑巖-矽卡巖型銅多金屬礦成礦地質背景與找礦潛力調查”(編號: 12120114068401)和西藏中瑞礦業發展有限責任公司項目(編號: XZZR-2015)聯合資助。

2016-02-27; 改回日期: 2016-04-02。責任編輯: 魏樂軍。

唐菊興, 男, 1964年生。博士, 研究員。主要從事礦床學和固體礦產勘查與評價研究工作。通訊地址: 100037, 北京市西城區百萬莊大街26號。E-mail: tangjuxing@126.com。

Abstract:Since the Paleogene (70–40 Ma), volcanic rocks of Linzizong Group have been distributed in a large area in Gangdise metallogenic belt, Tibet; nevertheless, there is an “absence” of mass resource and high economic value epithermal deposit except for the Qulong and Jiama porphyry-skarn copper polymetallic deposit (23–13 Ma) formed in the collision-stretch phase, in contrast with the Andean metallogenic belt (such as La Franja de Maricunga, Franja El Indio-Pascua) formed under the condition of extensive volcanic -magmatism. Are these deposits denudated or even not found yet? The authors have recognized a type of low sulfidation epithermal lead-zinc (In-Cd-Au) deposit in Linzizong continental volcanic rock group in Sinongduo of Namling basin, based on the detailed exploration, geological mapping, geological logging, microscopic examination, energy spectrometer analysis, electron microprobe analysis (EPMA) and the result of previous researchers. The orebodies consist of cryptoexplosion breccia type Ag-Pb-Zn orebody hosted in liparophyre, hydrothermal vein type Ag-Pb-Zn orebody beside volcanic edifice, and Ag (Pb-Zn) orebody on the hanging side of the fault. The amount of the controlled resource of Pb+Zn is over 0.3 million tons (331+332)@Pb+zinc＞5％, and resource amount of Ag@Ag＞50g/t is more than 400 tons. The major metallic minerals are galena, sphalerite, and argentite, pearceite, and pyrite together with rare chalcopyrite. Quartz-chalcedonite-jasper, siderite-rhodochrosite, barite-fluorite, and valencianite-illite-sericite are main associations of alteration. The main structures include veined sturcture, brecciated, mesh-veined, banded and laminated, crustified, massive and disseminated structures, the ore textures of this deposit are developed on the basis of crystallization and metasomatism. The authors found a vent of ancient hot spring near the surface, around which there are some banded and laminated siliceous sediments. These geological findings led the authors to believe that this is a typical low-sulfidation epithermal Ag polymetallic deposit. This is for the first time a deposit of this significant type was found and verified in Gangdise belt and even in Tethys metallogenic province. The essentiality for guiding exploration in the area where Linzizong Group volcanic rock was developed in 70–40 Ma in Gangdise belt would be very obvious.