ON GRANITOIDS RELEVANT TO METALLOGENY

To begin with a general review about the argument upon the origin of granitoids since late eighteen century, this paper gives, at first, a brief account of the progresses in the granitoid studies approached from vareous aspects, especially in those made during the latest decade. As to the formation of granitoid, apart from the classical theory of residual differentiates from original basaltic mather magma, there are also other conceptions such as anatexis, palingenesis, ultrametamorphism, migmatization, granitization and partial melting of preexisting rocks, formulated by separate authers from discrete regions at different times. Although the intents of the vareous conceptions are somewhat different, but they all imply that the pre-existing rocks appeared to have been transformed, to some extent, into a sort of melt （hot fluid） at the ultimate stage of vareous processes. Such melt would give rise to consistent geological effect as original magma should do. Granitoids may be crystallized from the original magma or the neo-melt in more or less the same way. In this sense, this paper, then, tries to deal with the relationship between granitoids and metallogeny in China. Based upon the present documents available, the granitoids of Chinese Continent can be tentatively generalized, according to their characters and mode of occurence in different tectonic units, into three major groups: （A） Large batholiths in faulted fold systems are usully elongated in form, parallel to the fold structure, locally marked by cutting the structure. They are, mostly made up of equigranular masive granitoids. Some have megacrystals in addition and some others show, themselves, foliation structure which look much like that of the adjacent metamorphic rocks. Still, some appear to gradually merge into the country rock. Many such granitoid batholiths are associated with pigmatite or migmatite. （B）Small batholiths, stocks and intermitently stretching irregular small masses distributed along fracture zones or deep faults, are mostly composed of medeum grained crystalline rocks characterized by such features as resulted from fractional crystallization and some marginal assimination of coutry rocks. Around the intsusive body usually presents contact metamorphic aurole of vareous tactites as Skarn, hornfels and marble etc. and the grade of metamorphism remarkably decreases away from the intrusive. （C）Anorogenic sporadic small intrusive or subvolcanic bodies located in either the above stated two kinds of igneous masses or the country rocks are represented by equigranular to porphyritic rocks. Country rocks around the intrusive body usually show transformation of fracturing, crushing, breciation or crumpling. There may be some contact aurole in carbonate and mafic country rocks but obscure in felsic country rocks. As a result of spatial and temporal analysis of Granitoids, six remarkable points about the metallogy of China have been put forward as follows: （1） Whatever be their origin, granitoids do provide not only heat but also some ore materials for the formation of ore deposits. Different metal association appears to be given off from different variety of granitoid. For example, siderophile metallic elements often show affinity to mafic granitoid as diorite while lithophile elements, to subalkalic, ultra-acidic granitoid. （2） Much more ore deposits of vareous types have formed along with tectono-magmatism since Yenshanian movement than those prior to the movement. There are scarecely any yenshanian granitoid related to metalliza tion in the terrain to the north of Kunlon mountain range and west of Yenchuan-Longmenshan fracture zone. it seems, therefore, resonable to take the Yinchuan-Longmenshan-Kunming tracture zone as the boundary between West China and East China metallogenic domains. （3） The nearly east-west trending faulted fold system, contractive in nature,and the north-northeast trending fracture zones, expansive in nature, are the major tectonic factors controlling magmatism as well as metallogeny. The East China metallogenic domain is characterized by"tectonic framework bone"except for Taiwan Cenozoic fold system. Those areas where the two sets of the major tectonic units intersect each other are usually rather concentrated with ore deposits than elsewhere. It is in those areas where occur multi-metallizations, i. e. earlier metallization super-imposed by later ones, and hence metallogenesis get enhanced. （4） Take the East China metallogenic domain as an example. The palaeo-China continent appears to be an axial plate from which the development of granitoid down to the south underwent rather different process as compared to that occurred up to the north. Although the temporal evolution of magmatic activity tends to be, as a rule, from basic to acidic and finally alkalic in nature during every vigorous movement since the end of Archaen to Yenshanian, the spatial variation of the most developed Yenshanian granitoids appear remarkable in different metallogenic provences of South, North and Northeast China. In South China, the granitoid is represented by granodiorite-monzonitic granite-Biotite granite rock series dominant in biotite granite. In North China massif（eastern part of palaeo-China continent）, the granitoid consists of diorite with lots of Gabbro inclusions,quartz diorite-admellite-monzonitic granite-granite rock series. Still present are many syenite bodies. But, in Northeast China metallogenic province, the intent of Granitoid is biotite granite—alaskite-potash granite-granosyenite rock series. The different rock series should reflect themselves different in origin and in relevant developing process and, therefore, different in ore element association. （5） It is clear that a great amount of ore deposits is often associated with smaller granitoid bodies rather than with large batholiths especially those elongated belt-like batholiths. No recognizable metalic zoning has been found around the large batholith, bul there is evidental ore zoning around small ingeous bodies. It is highly probable that the small bodies may be the apex of concealed large intrusive as revealed by air photo in many cases and rich in volatile flux ascending from below. However, most of the large batholiths are compsite and made up of multiple phases of intrusion. It is still possible to find anorogenic small intrusive bodies or hydrothermal altered areas and corresponding ore deposits within the batholith. （6） Associating with W. Be. Nb, Ta and rare elements, the tin is commonly believed to be of continental crust origin. In south China metallogenic province, separate tectonic movements took piece at the end of proterozoic, caledonian, Hereyno-Indosinian and Yenshanian periods from west to east successively. Near the late stage of each movements, always formed tin deposits in affinity to granitoid. But most of the significant tin deposits occurred properly during Yeushanian. Many Chinese geologsts have proposed that the granitoids relevant to tin deposits in South China might have originated from rather deep sources of Precambrian or Lower Palaeozoic rocks. While the rocks were involoed in the process of partial melting, the tin originally in them might get activated too. Repeated melting gave rise to repeated tin enriching and till Yenshanian the enrichment attained such a high grade as to make the granitoid able to form economic tin deposits.However, the recent discovory of subsea tin mineralization at the midridge of the Atlantic Ocean indicates that the ultimate source of tin, same as other metals, should be attributive to mantle rather than crust.