高级矿床学8找矿案例斑岩矿床ppt课件.ppt
高级矿床学-斑岩型矿床斑岩铜矿斑岩铜矿(Porphyry copper deposits)为世界提供了 50%以上的铜金属(over 100 producing mines)。Their close relatives the porphyry moly deposits produce 70%of the worlds moly.Both deposit types will be discussed separately,but they share many characteristics and are formed in somewhat similar manners.全球斑岩铜矿分布图绝大多数斑岩铜矿形成于中新生代，与离散板块边缘上及附近的火山链有关（环太平洋、古地中海和古亚洲洋）。极少数为古生代，分布在古生代板块边缘上，如U.S.S.R、United States。全球已知最大的88个斑岩铜矿产于美国西南部，成矿时代为58-72 Ma。岩体形态岩体形态典型斑岩铜矿床呈圆筒状，产于岩株状岩体中，出露面积为1.5 x 2 km（椭圆状），核部为斑岩质，向外到边部为中粗粒等粒的成分相似的岩石。主岩岩石学主岩岩石学一般地，容矿主岩为长英质侵入体，成分为石英正长岩、石英二长岩、花岗闪长岩系列；闪长岩正长岩系列热液蚀变热液蚀变Lowell and Guilbert 总结的斑岩铜矿蚀变模式，围绕斑岩株依次出现4个蚀变晕钾化带-都存在。特征：次生的钾长石、黑云母和/或绿泥石交代原生的钾长石、斜长石和镁铁质，及微量的绢云母。绢英岩化带 可存在。特征：脉石英、绢云母、黄铁矿和微量绿泥石、伊利石和金红石，交代钾长石和黑云母。泥化带（Argillic）-可存在。特征：高岭石、蒙脱石等粘土矿物及微量浸染黄铁矿。斜长石强烈蚀变、钾长石不受影响，黑云母绿泥石化。青盘岩化带（Propylitic）-都存在。特征：绿泥石、方解石、微量绿帘石。镁铁质矿物强烈蚀变，斜长石消失。在深部，上述各带融为一体，构成石英-钾长石-绢云母-绿泥石组合。Hypogene Mineralization矿体产出环境:1）整个岩株内；2）部分岩株部分围岩；3）仅在围岩内矿体通常为陡壁圆筒状，也有板状、扁圆锥状（tabular to flat conical）矿化为浸染状或细网脉状，铜品位0.4-1%Cu，含微量Mo 和 gold。矿化呈带状：Inner Zone 与钾化带吻合，一般直径数百米，相对地硫低，但钼最高。黄铁矿 2-5%，py/cp比约 3:1。矿化为浸染状而非细网脉状。Ore Zone 大致分布在potassic-phyllic 带边界上，黄铁矿 5-10%，py/cp 比约 2.5:1。主要矿物为黄铜矿，呈细网脉状。其他矿物有斑铜矿、硫砷铜矿和辉铜矿。Pyrite Zone 包括phyllic and argillic(若存在)的大部。黄铁矿相当高，可达 10-15，py/cp 比约 15:1。矿化即有浸染状又有脉状。许多附加的外来硫化物相开始出现在上部。Outer Zone 与 propylitic zone吻合。黄铁矿微量，铜矿物稀有。闪锌矿和方铅矿常见，但常为边界品位级。矿化为脉状。Breccia Zones-Often major ore carriers in the porphyry system.Have very high grades(2-5%Cu)and can occur both in the porphyry or the country rock.May be formed by hydrothermal activity,gravitational collapse or later explosive volcanism.在成矿区带上，斑岩铜矿、钼矿和锡矿明显呈带状分布，与距板块俯冲带的距离有关，铜矿离海沟最近，而钼锡依次分布在海沟内侧。Vertical Extent of Porphyry Bodies斑岩铜矿与小高位小岩株和陆相钙碱性火山作用有关。因而侵入体为层火山所覆盖，青盘岩化延展到火山岩中，其它蚀变于其界面处。一般地，此模式说明斑岩铜矿是更大的成矿体系的一部分，包括高位浅成低温贵金属矿床。闪长岩模式闪长岩模式斑岩矿床有两个不同的体系：其一为“Lowell and Guilbert type”，以美国西南部以石英二长岩-花岗闪长岩为特征。其二为Andes and Pacific Islands.主岩为闪长岩，偶为正长岩。两者的特征对比见表。闪长岩体系的特征为：低硫逸度，存在磁铁矿，蚀变仅有钾化带和青盘岩化带，金为重要组分，而钼稀有或缺失。Comparison of the Lowell-Guilbert and Diorite Types of Porphyry Copper Deposits FEATURE LOWELL-GUILBERT DIORITE Host Pluton Quartz Monzonite to Granodiorite(S)Qtz.Diorite to Diorite(I)AlterationPotassicPhyllicArgillicPropyliticPotassicPropyliticMineralizationQuartz in fractures CommonCommonErraticOrthoclase in fractures CommonErraticMagnetiteMinorCommonPyrite in fracturesCommonLess CommonMolybdeniteCommonRareChalcopyrite/bornite3:13:1GoldRareImportantStructureBrecciaMay OccurRareStockworkImportantImportant这些差异可以理解为：日本岛弧侵入体没有斑岩铜矿，在岩相学上他们属于两类花岗岩（“S”and“I”type）。前者为陆壳深熔作用形成的，后者为板块俯冲期间部分熔融的最后阶段的分异产物。Characteristics of S&I Type GranitesFEATURE S TYPE I TYPEGabbro:diorite:granite2:18:8015:50:35Na2O(felsic)3.2%Al2O3/Alkalis+CaO1:1.706.704-.706NormativecorundumdiopsideAssoc.metalsSn,WAuGenesisCrustal anatexis of sedimentsPartial melt of mantleS and I type granites 的特征对比，与Lowell and Guilbert and Diorite 斑岩矿床所揭示的特征相似。闪长岩模式的矿床形成于大洋岩石圈俯冲所致的部分熔融作用，而 Lowell and Guilbert 模式矿床代表远离板块边界陆壳的熔融作用。成因成因典型斑岩体系的最明显特征是其大小。热液不仅渗透到母侵入体中，而且渗透至围岩中。认为容矿岩体侵入至浅部（0.5-2 km深)。侵入体结晶开始时，岩浆房的蒸汽压随不相容元素进入蒸汽相而增大，当蒸汽压超过上覆岩石的围压时发生退化沸腾。快速沸腾的液体最终克服岩石的拉伸强度从硅酸盐熔体中分离出来，导致强烈的网脉状角砾化(如:water at 2 Kb 压力和5000C的水由于沸腾体积增加至少 10%)。此外，沸腾是吸热反应，正在逸出的蒸汽膨胀时需要岩浆中的热，因而，快速降低了岩浆房中的温度,，形成侵入体中心的斑状结构。流体包裹体证据流体包裹体证据氧同位素研究表明 钾化带黑云母的值与岩浆水相当，而绢英岩化带的绢云母 亏损18O，表明为天水。泥化带也是如此。1）侵入体上升至地壳开始结晶；2）岩浆热液对流在侵入体内和附近形成钾化带；3）围岩中的天水对流形成青盘岩化，对流由侵入体热所驱动；4）随着侵入体的冷却，天水体系叠加至岩浆体系之上，形成 phyllic-argillic alteration zones。问题：1）为什么闪长岩模式矿床仅有potassic-propylitic alteration?2）为什么闪长岩模式岩浆水-天水系统从不互相侵入？Bingham Canyon,UtahLocationLies about 30 km southwest of Salt Lake City,Utah at an altitude of 2000 meters.From a historic perspective one of the most famous mines in the United States.Regional GeologyBingham is situated in the Basin and Range tectonic province.The Oquirrah Mountains form a horst block of folded Paleozoic rocks bounded by north trending faults.The principal country rocks are Pennsylvanian quartzites and limestones folded and intruded during the Mesozoic.The ore body itself occurs in one of a series of smaller horsts bounded by the northwest trending Bear and Occidental Faults which uplift the northeast trending Copperton Anticline.Mineralization is in or adjacent to the Bingham stock,a porphyritic granodiorite.The slightly younger(?)Last Chance stock to the south is barren.Both have been age dated at Eocene.There are three types of mineralization in the Oquirrah Mountainsalluvial gold Ag-rich galena and sphalerite veins in limestones porphyry copper mineralizationGeology of the Bingham Canyon Porphyry Copper DepositThe deposit occurs in a triangular zone of disseminated and veinlet copper sulfide mineralization 1.5 x 2.5 km in plan and at least 500 meters in thickness.The majority of the ore is in the granodiorite,but substantial reserves are present in the metamorphosed Paleozoics.The original host intrusive was a granodiorite,but subsequent hydrothermal alteration has resulted in a rock more closely approximating a granite.The stock has a well defined potassic alteration zone
