高级矿床学8找矿案例斑岩矿床ppt课件.ppt

《高级矿床学8找矿案例斑岩矿床ppt课件.ppt》由会员分享，可在线阅读，更多相关《高级矿床学8找矿案例斑岩矿床ppt课件.ppt（49页珍藏版）》请在三一办公上搜索。

1、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

2、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Lowell and Guilbert 总结的斑岩铜矿蚀变模式，围绕

3、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

4、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 an

5、d 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 b

6、e 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。,闪长岩模式斑岩矿床有两个不同的体系：其

7、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。,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。,S and I type granites 的特征对比，与Lowell and Guilbert and D

8、iorite 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

9、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

10、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 Mountain

11、s 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 O

12、ccidental 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

13、Oquirrah Mountainsalluvial gold Ag-rich galena and sphalerite veins in limestones porphyry copper mineralization,Geology 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 50

14、0 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

15、well defined potassic alteration zone characterized by secondary biotite,poorly defined phyllic alteration and a spotty and irregular propylitic alteration zone.Argillic alteration is absent.Extensive brecciation of both the intrusive and country rock is common.The primary mineralization averages 1-

16、4%of the rock.The core of the intrusive is moly rich with pyrite abundant only in the phyllic zone.Chalcopyrite and minor bornite are the only primary copper sulfides recovered.Peripheral skarn deposits consisting of enargite,galena,sphalerite and tetrahedrite are important in the surrounding metase

17、diments.Typical of most American deposits,early mining was from a supergene enrichment zone of chalcocite,malachite and native copper lying beneath a barren limonite cap 10-100 meters thick.Much of this supergene ore has been mined out.,GenesisNo specific genetic model has been proposed for the Bing

18、ham Canyon deposit.Rather its genesis is thought to be similar to that of all the southwestern porphyry copper deposits.,Porphyry Moly and Tin DepositsIn addition to copper there are other porphyly related types of mineralization,most notably molybdenum and tin.While each of the three types of porph

19、yry deposits contain appreciable quantities of the other elements,they are nonetheless geologically distinct enough to constitute end members of the porphyry spectrum.Originally it was thought that all moly deposits belong to a single group.It is now accepted that there are two subtypes.The nomencla

20、ture is confusing since one type is termed simply porphyry moly while the second type is the Climax type.,Porphyry Moly Subtype1）与花岗闪长岩石英二长岩类I型花岗岩有关。与I型斑岩铜矿（闪长质）相比，略显酸性。矿物只有辉钼矿，脉状和浸染状，品位低(0.1-0.2%MoS2)。2）蚀变不易识别，但钾蚀变普遍。由于岩石富钾，难以识别钾化。有些硅化仅出现在钼矿脉周围。Ore bodies are sheet-like to tabular.Deposits range in

21、 age from 30-80 MY and occur in association with Mesozoic to recent subduction zones,particularly those with steep angles.No simple genetic model seems to fit all of the deposits in this subgroup.Clearly they are related to subduction and evidence from fluid inclusions and isotopes favors a genesis

22、similar if not identical to the diorite type porphyry copper deposits.An unanswered question is the relationship of the moly deposits to the copper deposits.Quartz Hill in Alaska lies less than 50 km from an active trench leading some geologists to suggest that porphyry moly deposits form at shallow

23、er depths nearer the trench than do porphyry copper deposits.However,in the Andes where both moly and copper deposits have been extensively mapped the moly deposits lie in a belt to the east of the copper deposits and farther from the trench.Unfortunately,age differences between the copper and moly

24、belts as well as changes in the angle of subduction complicate the picture in the Andes.,Climax Type Moly DepositsClimax type 钼矿与A型(S型亚类)花岗岩有关。其与S型不同点是富K2O 和F。矿体均在岩体中，辉钼矿为主矿物，但可回收锡钨。品位高于斑岩钼矿，平均约0.35%MoS2,某些矿床高达0.7%。蚀变为弥散型，强烈的硅化及钾化、青盘岩化、磁铁矿-黄玉化，偶见弱的绢英岩化/泥化。矿体为伞形。成矿年龄约 30 Ma。已知的 Climax type moly depos

25、its 位于西 Cordillera,大致从中 Montana 至北 New Mexico。若与中生代俯冲带有关（尚有争议），矿床则分布于板缘 1000 km内。A-type 或非造山花岗岩认为是大陆裂谷的产物（尚有争议）。另一可能性是与俯冲有关,矿床形成在俯冲浅角度的地区。锶同位素比大于0.706，常超过 0.740。高氟说明陆壳混染。俯冲带深部的热使加厚的陆壳基底发生熔融。这些岩浆慢慢混染陆壳物质而富集K和Mo。,Climax,Colorado位置位于Denver西部约100 km，海拔 4000 m的陆地分界线。概述位于Colorado Front Range，由元古代片岩和片麻岩(Id

26、aho Springs Group)所组成，被元古代Sliver Plume Granite所侵入。Front Range构造复杂，但褶皱却以北东向为主。古生代沉积岩不整合于元古代基底之上。Mosquito Fault切割Climax岩株，为区内主要断裂，它从古生代活动至今。早第三世浅侵入体和流纹质火山作用是本区最后的地质事件。Geology of the Climax Deposit主要矿化带直径约1.5 km，成为了侵入于Idaho Springs Group中的岩株和岩脉的顶帽。Mosquito Fault 切过矿带的西部。4个岩体控制了矿化，时代为Oligocene 世。岩株西南部最老

27、，次为中央岩株，共同构成了 Climax 花岗闪长岩体。最后它们被 Aplite Phase and the Porphyritic Granite所侵入。,Alteration consists of early potassic alteration,weak sericitic alteration and late,intense silicification.Four phases of mineralization are recognized,each correlated with an intrusion.The first three form the thick umbr

28、ella-like ore bodies(Figure).The earliest,and uppermost,Ceresco ore body has been almost completely removed by erosion.Beneath the Ceresco lie the Upper and Lower(younger)ore bodies,correlating with the second and third intrusions.The fourth intrusion produced silicification,but no mineralization.Mi

29、neralization consists of a zone of irregular veinlets containing quartz,K-spar and fine-grained molybdenite.Some ore occurs in larger veinlets(pseudo-pegmatites)and along joint surfaces.Fluorite and topaz are common accessory minerals,as are wolframite,pyrite and cassiterite.GenesisThought to be sim

30、ilar in many respects to porphyry copper deposits,however the rocks are more silicic suggesting either significant crustal contamination or an entirely crustal origin for the intrusives.While some copper deposits occur in settings suggestive of multiple intrusive phases there appears to be only a si

31、ngle ore body,in marked contrast to moly deposits where each intrusive has an associated ore zone.,Tin DepositsPorphyry tin deposits are restricted to a linear belt in the Andes Mountains east of the copper-moly belts.Host intrusives are generally latite porphyry stocks to true granites.There is a c

32、lose association with stratovolcanoes indicating very shallow levels of emplacement.Rather than the typical flaring stock,intrusions associated with tin deposits appear to be narrow finger-like projections.The main ore mineral is cassiterite,ore grades averaging 0.1-0.2%SnO2.The ore occurs as an ear

33、ly disseminated phase that is sub-ore grade followed later veins.Alteration consists of silicification,sericitization,propylitization and deep level quartz-tourmaline.There is an absence of potassic alteration.In some instances,there are associated peripheral base metal vein-type deposits.,GenesisTh

34、ought to be a two stage model(Figure).Emplacement of shallow plug-like stock in the vent of a felsic stratovolcano.Magmatic-meteoric water system develops as igneous activity wanes causing pervasive alteration and the disseminated tin mineralization.As temperature declines cooling causes fracturing

35、of the rocks.These fractures widen and deepen eventually tapping the deeper magma chamber feeding the volcano.This allows volatiles to escape the chamber and stream upward.Cooling causes deposition on fracture walls generating the vein-type tin mineralization.,Characteristics of Porphyry Cu-Mo-Sn De

36、posits1Restricted to the Phanerozoic(mostly Mesozoic-Tertiary).Closely associated with felsic intrusives of qtz diorite to qtz monzonite composition.2Accompanied by characteristic alteration envelope.potassic-phyllic-argillic-propylitic.3Strong zoning in relationship to plate boundaries.Cu Mo Sn mov

37、ing inland from the plate margin.4Closely associated with island arc development and subduction zones at convergent ocean-continent plate boundaries.5Ore occurs in a large,low-grade shell adjacent to the potassic zone.Chalcopyrite and bornite most common minerals with lesser molybdenite and cassiter

38、ite.6Isotopic evidence suggests shallow depths of magma generation and significant groundwater interaction.,Vein-type DepositsThese were once one of the most sought after and heavily mined types of ore deposits.The famous mining districts of the West are mainly vein-type deposits.Vein-type deposits

39、represent a progression into true hydrothermal deposits that lie at some distance from the igneous source.Today this group has declined markedly in importance,but still produces much of the worlds silver and tungsten and some gold and base metals.The search for this type of deposit has been abandone

40、d largely because they tend to be small and difficult to find.Lindgren Classification-Still much in vogue for the description of vein-type deposits(See Handouts for Hypothermal,Mesothermal and Epithermal deposits).These handouts date from the 1930s,but with the exception of temperature data,the info

41、rmation has changed very little.,General CharacteristicsAlthough as a group the deposits vary considerably in size,mineralogy and geologic environments,all have certain unifying features:association in space and time with calc-alkaline igneous activity;clearly epigenetic with ores having vein-like f

42、orm and close spatial relationship to faulting;ore minerals are deposited as open space filling along dilatant zones or as replacements of carbonate host rocks;zonation is characteristic and always present(Figure);deposition is from hydrothermal fluids at depths of less than 3 km;sulfur is usually o

43、f magmatic origin(34S=0);districts are structurally complex;some form of alteration is always present,often sericitic at a minimum;often see a progression from magmatic water to meteoric water later in the paragenetic sequence.,Various more recent classifications of vein-type deposits have been prop

44、osed,but none have been adopted uniformly.Most geologists have switched to type groups of deposits(e.g.Carlin-type,Creede-type).This often leads to a certain degree of confusion.,Mesothermal Base-Metal VeinsOccur in rocks of all ages,but most important districts are of Paleozoic/Mesozoic age.Seem to

45、 be restricted to orogenic belts,in particular the Rocky Mountains.As such,the western Cordillera is famous for the concentration of this type of deposit.FormMost of the large deposits are replacement-type associated with major fault systems.Overall the shape of most districts is linear reflecting t

46、he strong control faulting has on ore deposition.Setting矿床与钙碱性火山作用及其侵入体密切相关，尽管大部分地区地质情况复杂，但成矿时代却集中在侵入事件的峰期后不久。典型岩株为浅成相石英闪长岩至花岗岩。断裂作用是区内主要特征，可填出至少一条区域断裂。一般地矿体与主断裂无关，但与其平行的次级断层或年轻的交切断层有关。,Alteration变化大，决定于主岩性质。砂岩中蚀变限于矿脉两侧数厘米，而碳酸盐内可达数千米。碎屑岩内为简单的硅化，而碳酸盐和变质岩内有绢英岩化+泥化+青盘岩化。蚀变通常是复杂的，难以区分，特别是脉体之间的蚀变相互叠加。Min

47、eralogyCu,Fe,Pb,Zn 硫化物为主，次为硫盐矿物。常见矿物为黄铁矿、黄铜矿、斑铜矿、方铅矿、闪锌矿、砷黝铜矿tennantite、黝铜矿tetrahedrite、硫砷铜矿enargite、辉铜矿 chalcocite 和蓝辉铜矿digenite。磁黄铁矿缺失，由此限定了其上限。所列矿物大多是银的重要载体，为世界银资源的主体。共生序列极其复杂，显示其形成历史长。在中温区沿走向矿物分带，从而呈现出亚带来。Gangue脉石矿物种类少，主要为方解石、石英、菱铁矿、白云石、铁白云石,Geochemistry流体包裹体表明成矿温度为250-4000C，盐度较低(1-4 wt%)。稳定同位素数

48、据支持岩浆硫的观点，说明至少早期矿物与岩浆水有关。GenesisEarly genetic models suggested that the major faults within the districts served as conduits for magmatic waters which flowed along the faults in search of easily replaceable rocks(carbonates)where deposition occurred.This model is not without its problems.First stabl

49、e isotopes indicate that in many districts meteoric water has played a substantial role.Second there is the problem of carrying sulfur and ore minerals in the same fluid.Despite these problems the model has been little changed or modified.The lack of emphasis on these deposits in recent years is pro

50、bably a major reason for the rather incomplete model.For instance,compare them to epithermal deposits that will be discussed in a separate lecture.Models for epithermal deposits are complex and leave few unanswered questions.,Coeur dAlene District,IdahoThe Coeur dAlene district is one of the most fa