Acid magmatism and related metallogenesis in the Erzgebirge

Abstract

In the Erzgebirge two post-collisional Hercynian granitoid complexes are developed: an older one, monzogranitic, moderately specialized, Sri =0.7064-68, &TNd = -1.8 to -6.2, lg f0, < -13 f 1, Ig fHF/fH20 = -3.9 f 0.2, S-type, 340-325Ma in age, and a younger one, monzo-to albitegranitic, highly specialized in Li, Rb, Cs, Sn, and W, Sri disturbed by strong autometasomatic influences, ET,, = -3.8 to -6.0, lg f02 < -17 f 1, lg MF/fH,O = -3 f 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 f0, but low fHF/fH,O, the tin-bearing younger association, in contrast, is controlled by low f0, coupled with high MF/fH20.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 solutions or, increasingly, by leaching of specialized magmatites. KEY WORDS Hercynian magmatites Leucocratic metallogenesis Melanocratic metallogenesis Tin mineralization

Geochemical specialization of the tin-bearing granitoid massifs of NW Bohemia

“…Fiala (1968) defined transitional granites on the basis of studies in the Slavkovsk) les Forest Mts. Detailed classification into intrusive complexes and phases has been elaborated in Saxonia (most recently by Tischendorf et al 1989). This classification is based on the theory of main and additional intrusions (Koptev-Dvornikov 1952), which are distinguished according to the grain size.…”

“…While the Nigerian biotite granites have Sri values more than 0.705 (0.708 0.752) (van Breemen et al 1975), young granites of Krugne hory (both west and east) have Sri values less than 0.700 (Tischendorf et al 1989). …”

“…Here, two major granite types were differentiated more than one hundred years ago (Laube 1876): the older, unmineralized "mountain granite" (Gebirgsgranit), nowadays often termed the "older intrusive complex" (330-320 Ma), and the younger, orebearing "Krugn6 hory granite" (Erzgebirgsgranit) now classified as the "younger intrusive complex" (305 295 Ma, ages after Tischendorf et al 1989). Transitional granites connecting the two main types, were discovered in the Slavkovsky les Forest by Fiala (1968).…”

“…Transitional granites connecting the two main types, were discovered in the Slavkovsky les Forest by Fiala (1968). Previous investigations of granite differentiation in NW Bohemia were mainly based on petrographically distinguished granite types (Lange et al 1972;Baumann et al 1974;~temprok 1987;Tischendorf et al 1989). There is a certain deficiency in this aproach as the granites of NW Bohemia are mineralogically relatively monotonous, but texturally very diversified.…”

The origin of Kibaran (late Mid-Proterozoic) tin, tungsten and gold quartz vein deposits in Central Africa: a fluid inclusions study

“…The tin granites are sub-alkaline, strongly peraluminous equigranular biotite-muscovite granites or muscovite alaskites with normative corundum to 5 wt %. The rocks display the typical enrichment in Li, Cs, Rb, B, F and Sn of specialized granites (Lehmann and Lavreau 1988), although at a moderate level compared with Hercynian lithium granites of the Erzgebirge/Central Europe (Tischendorf 1989). Similar to other post-orogenic gran- Mi-Miyove Au; N v-Nyungwe Au; Ci-Cibitoke Au; Mu-Muyinga Au.…”