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太古宙金成矿作用的最终解决,认识上有赖于如下两方面的一致进展(1)绿岩带的成因(2)金矿床的成因。为此,本文总结了目前有关太古宙火山岩岩石成因的知识和有关加拿大地盾苏必利尔省太古宙绿岩带中金矿化特征的知识。二个太古宙绿岩带中痕量元素地球化学的研究确认并详述了火山旋回的基本概念,每一旋回都由底部拉斑玄武岩(TH)和上部钙碱性岩(CA)构成。某一火山岩堆积既可为单旋回的(TH-CA)也可为多旋回的(重复TH-CA)。所有的火山岩组分表明都直接来源于地幔。CA和TH英安岩和流纹岩很易解释为安山质—玄武质母岩分离结晶作用的产物。由痕量元素研究表明的另一套基本特征是,亏损的或未亏损的地幔源产生的火山旋回可共生出现。这些限制导出了一个与地幔脉动底辟有关的成因模式。每一旋回运动的早期,一亏损地幔层上部的熔融提供TH系列,此后,底辟活动(包括最初较深但由于底辟现已升起的未亏损岩层的熔化)提供了CA岩系。因此,绿岩带发育应归因于一个脉动移动的地幔卷流体系,即一种使多相地幔受影响的“热点”构造类型。苏必利尔省西部二个绿岩带中292个火山岩中痕量金的丰度表明,小于1PPb的含金量绝大多数在0.2—225PPb范围内,平均为7.4PPb,中值为3.2PPb。通常镁铁质—中性火山岩含金较高,尽管偶而在英安岩—流纹岩中出现高值。金含量与痕量金属(Cu、Pb和Zn)相关,但与挥发分(CO_2、H_2O和s)不相关。金的高含量特别出现于长英质—中性火山岩堆积的上部层序中。该特征与太古宙火山岩堆积上部层序中的Au和贱金属硫化物矿床的富集特征一致,这些太古宙火山堆积通常大量伴生有长英质火山岩。这种分布特征是否反映了(a)初期岩浆成因,(b)火山岩的海水淋滤,(c)在变形和变质作用期间变质分泌作用和扩容带中的富集或(d)是上述几种作用相互的结合或按顺序的联合?这些仍远未解决,确是应进一步解决的课题。然而上面引证的“多旋回分离结晶作用”火山作用特征提出了一个很有意义的初期岩浆作用,这种作用可能和其它特定作用过程有关。
The ultimate solution to the Archean gold mineralization is based on the following two developments: (1) the genesis of the Greenstone Belt (2) the genesis of the gold deposit. For this reason, this paper summarizes the current knowledge about the genesis of Archean volcanic rocks and the knowledge of gold mineralization in the Archean greenstone belt of the Superior Shield, Canada. The study of trace element geochemistry in two Archean greenstone belts confirms and details the basic concepts of volcanic cycling, each of which consists of bottom threshing basalts (TH) and upper calc-alkaline rocks (CA). A volcanic rock can be either single-cycle (TH-CA) or multi-cycle (repeat TH-CA). All volcanic components indicate that they are all directly from the mantle. The CA and TH dacite and rhyolite are easily interpreted as the product of the separation crystallization of andesitic-basaltic parent rock. Another basic feature demonstrated by trace element studies is that volcanic cycles generated by depleted or unexposed mantle sources can occur symbiotically. These constraints lead to a pattern of genesis related to the fluctuating diapirs of the mantle. Early in each cycle of movement, a series of depleted depleted mantle upper fractions provide the TH series, after which the diapiric activity (including the initial deep but melted non-depleted rock that has risen since the diapir) provides the CA series. Therefore, the development of greenstone belts should be attributed to a pulsating mantle tugal system, a type of “hot spot” that affects multiphase mantle. The abundance of trace gold in 292 volcanic rocks from two greenstone belts in western Superior Albino suggests that the majority of gold less than 1 ppb is in the 0.2-225 ppb range with an average of 7.4 ppb and a median of 3.2 ppb. Often the mafic-neutral volcanic gold is higher in gold, albeit occasionally with high values in the dacite-rhyolite. Gold content correlates with trace metals (Cu, Pb and Zn), but not with volatiles (CO 2, H 2 O and s). In particular, the high gold content occurs in the upper sequence of the Changying-Neutral Volcanic Deposit. This feature is consistent with the enrichment characteristics of the Au and base metal sulphide deposits in the upper Archean volcanic sedimentary upper sequence, which are often associated with a large number of long-felsitic volcanic rocks. (A) initial magmatic origin, (b) seawater leaching from volcanic rocks, (c) metamorphism and metasomatism during deformation and metamorphism, or (d) enrichment in these zones The combination of the functions of each other or in sequence? These are still far from being resolved, and indeed they should be further resolved. However, the volcanism characterization of “polycyclic segregation crystallization” quoted above suggests a very meaningful primary magmatic activity that may be related to other specific processes of action.