摘要:

AbstractField relationships of three types of granitoids with basic rocks, with different mineralogy and structure are described. Zones of mixed‐type character exist between the several types of granitoids as well as between the granitoids and basic rocks. The distribution of magmatic mafic enclaves (MME) in the granitoids varies widely but the largest concentrations occur in the mixed zones between the granites and basic bodies. The origin of such enclaves is closely related to processes of hybridization and mingling of acid and basic magmas. One of the possible variants of such interaction is the fragmentation and partial hybridization of synplutonic basic dyke

ISSN:0072-1050    

DOI:10.1002/gj.3350250322

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA new database of some 200 granitic bodies throughout the world associated with Sn, W and Mo deposits is analysed with respect to size and petrological characteristics. Most Sn, W and Mo deposits relate to small stocks not exceeding 25 km2. Biotite granites are the most common type of ore‐bearing plutons, while two mica granites are subordinate. There seems to be an upward grading in grain size such that the later, higher members of a suite are the finest grained. Ore‐bearing processes relate to deep evolving differentiation of specialized magmas modified by mantle flu

ISSN:0072-1050    

DOI:10.1002/gj.3350250323

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractTextural evolution from coarse K‐feldspar megacrystic granite, through heterogeneous granite porphyry to microgranite corresponds to a sequence of geochemical evolution. It was probably triggered by a sudden loss of pressure, resulting in quenching, fluidization, and disruptive emplacement of the residual melt into the partially or wholly crystalline host granite. It was accompanied by alkali metasomatism, volatile‐fluxing, and hydrothermal alteration, culminating in the formation of greisen bordered vein swarms and massive greisens mineralized with tin and other met

ISSN:0072-1050    

DOI:10.1002/gj.3350250324

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe genesis of granites enriched in Sn and U and their role in the formation of Sn–U deposits is reviewed with particular reference to studies of geochemical, geophysical, and geological data sets from the Scottish Caledonides based on image analysis studies.The chemistry and tectonic setting of radioelement‐enriched granites some of which are also enriched in Sn (e.g. Cairngorm intrusion) is distinct from that of the more commonly occurring calc‐alkaline granites. On mantle‐normalized diagrams they are enriched in U, Th, Rb, Nb, Ta, Li, F, Be, B, and Sn with marked depletion of Sr, Ba, Ti, and P; and on chondrite normalized REE diagrams they have high REE with LaN/LuNvalues of 1·8–6 and marked negative Eu anomalies (Eu/Eu* 0·3). These features are characteristic of Sn–U granites from S.W. England (Dartmoor) and elsewhere. Geophysical data indicate that the Caledonian Sn–U granites are the high points of a buried batholith (the East Grampian batholith) with a length of approximately 100km, breadth of about 40km, and depth of approximately 7–8km. The batholith is discordant to the Caledonian structural grain and was emplaced post‐orogenically, probably in tensional pull‐apart structures.Petrogenetic models and isotopic data for the Cairngorm granite preclude ‘S’‐type crustal melting models for its genesis; instead the preferred model involves combined assimilation and fractional crystallization (AFC) as the result of the addition of dioritic magma to the lower crust followed by up to 50 per cent fractional crystallization. The concentration of Sn, F, and radioelements in the granite magmas, the release of heat as the result of protracted fractionation, the large volumes of the intrusions, and their emplacement into fault systems are factors favouring the formation of Sn and U deposits. The high calculated heat production of such intrusions and their emplacement into faults along which reactivation can occur may explain the association of such granites with hydrothermal ore deposits formed long after magmatic cooling.Overall the role of granites in ore formation is complex and reflects such factors as the chemistry, heat production (contents of U, Th, and K), density, permeability, and response to deformation of intrusions as well as the availability of water in the rocks i

ISSN:0072-1050    

DOI:10.1002/gj.3350250325

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn the Erzgebirge two post‐collisional Hercynian granitoid complexes are developed: an older one, monzogranitic, moderately specialized, Sri= 0·7064–68, εTNd= ‐1·8 to ‐6·2, 1g fO2<−13 ± 1, 1g fHF/fH2O = ‐3·9 ± 0·2, S‐type, 340–325 Ma in age, and a younger one, monzo‐ to albitegranitic, highly specialized in Li, Rb, Cs, Sn, and W, Sridisturbed by strong autometasomatic influences, εTNd= −3·8 to −6·0, 1g fO2<−17 ± 1, 1g fHF/fH2O = ‐3 ± 0·3, I‐type, 310–295 Ma. Postplutonic volcanics (rhyolite, rhyodacite, latite, kersantite–minette) in each case complete the magmatic sequences.Muscovite–wolframite–molybdenite–pyrite–quartz association is locally related to the older complex, but numerous centres of cassiterite–wolframite–zinnwaldite (or muscovite) deposits are related to the younger one. Both mineralizations are of orthomagmatic origin and underwent strong physicochemical control. Thus, the granites genetically related to the tin‐free older association are conditioned by medium fO2but low fHF/fH2O, the tin‐bearing younger association, in contrast, is controlled by low fO2coupled with high fHF/fH2O.Vertical compositional zonation in magma chambers caused enrichment of compatible elements such as Zn, Pb, Mg, Ca, Ba, Sr, in deeper parts of the chamber and their transition into residual solutions which then may form base metal mineralization as cross‐cutting veins. Mineralization events last up to the Triassic. Probably elements in the later stages were derived either from deep‐originated residual

ISSN:0072-1050    

DOI:10.1002/gj.3350250326

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350250301

出版商:John Wiley&Sons Ltd    

年代:1990

数据来源: WILEY