Geochemistry of Feldspars and Muscovite in Granitic Pegmatite From the Cap De Creus Field, Catalonia, Spain

Abstract

The Cap de Creus pegmatite field exhibits a well-defined regional zonation of four types of granitic pegmatite: barren Kfeldspar-rich pegmatites (type I), beryl-columbite-subtype pegmatites (type II), beryl-columbite-phosphate-subtype pegmatites (type III) and albite-type pegmatites (type IV). There is an increase in the albite content, relative to K-feldspar, with increasing pegmatite evolution. Type-I microcline-rich pegmatites have low contents of albite, whereas in type IV, albite is the only feldspar. The K/Rb value in K-feldspar decreases progressively from type-I to type-III pegmatites. In addition, there is a progressive enrichment in P, Rb, Cs, Y, Sr, Ga, Ce, W and Sn from type-I to type-IV pegmatites. Concentrations of Pb and Zr decrease in Kfeldspar from type-I to type-III pegmatites. K-feldspar from the Cap de Creus pegmatites exhibits higher contents in Ba, Rb, Cs, Nb, Y, Sn, V and Cr than albite. Albite is richer in Sr, Zr, Cu, As, Ce and Ga. Pb, Zn, W, Co and Ni have similar affinity for Kfeldspar and albite. Muscovite exhibits similar geochemical evolution to K-feldspar. These progressive trends suggest a common origin for all of the Cap de Creus pegmatites by fractionation of the same parental magma. The high P content of feldspars, up to 1.67 wt.% P 2 O 5 in K-feldspar and 1.75 wt.% in albite, indicates buildup in this element from the earliest stages of pegmatite crystallization. Trace-element variation in feldspars and muscovite reflects enrichments in the melt; a higher content correlates with characteristic minerals of these elements. In particular, the phosphorus content of albite is proposed as a useful mineralogical guide to niobium-tantalum-rich oxide mineralization. SOMMAIRE La suite de pegmatites granitiques du Cap de Creus démontre bien une zonation régionale dans la disbtribution de quatre types de pegmatite: pegmatites stériles enrichies en feldspath potassique (type I), pegmatites du sous-type à béryl-columbite (type II), pegmatites du sous-type à béryl -columbite -phosphate (type III), et pegmatites à albite (type IV). Il y a une augmentation progressive de la teneur en albite par rapport à celle du feldspath potassique, avec le degré de fractionnement. Les pegmatites du type I, riches en microcline, ont une faible teneur en albite, tandis que dans les pegmatites de type IV, l'albite est le seul feldspath. La valeur de K/Rb du feldspath potassique diminue progressivement des pegmatites du type I à celles du type III. De plus, il y a un enrichissement progressif en P, Rb, Cs, Y, Sr, Ga, Ce, W et Sn du type I au type IV. Les concentrations de Pb et Zr diminuent dans le feldspath potassique des pegmatites du type I à celles du type III. Le feldspath potassique des pegmatites du Cap de Creus fait preuve de teneurs plus élevées en Ba, Rb, Cs, Nb, Y, Sn, V et Cr que l'albite. En revanche, l'albite est plus riche en Sr, Zr, Cu, As, Ce et Ga. Le Pb, Zn, W, Co et Ni ont un degré d'enrichissement semblable dans le feldspath potassique et l'albite. La muscovite fait preuve d'enrichissements ...

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Determination of Metals and Metalloids in Marine Sediments. Evaluation of the Contamination Levels in Tenerife Island

“…0.95) exists between Cs-Rb, Cr-V, Ni-Co, Pb-Ba, population-Pb, and population-Rb. These relationships between elements have been reported in previous correlation studies, Cs and Rb especially in igneous rocks (Alfonso et al 2003), and also Cr-V (Mielke et al 1999) and Ni-Co (Kay and Conklin 2001). Figure 2 shows the correlation graph between the strongest correlated elements.…”

Mineral chemistry, petrology and geochemistry of the Sebago granite-pegmatite system, southern Maine, USA

“…Geochemical indicators, such as K/Rb and K/Cs in K-feldspar and micas, Nb/Ta in columbite group minerals, Zr/Hf in zircon and Fe/Mn in garnet, serve as important tools which, along with field relationships, have proven invaluable in establishing fractionation trends of rareelements in individual pegmatites and granite-pegmatite systems (e.g., Trueman and Černý 1982;Černý et al 1985;Černý 1991) and developing models for the petrogenesis and evolution of granite-pegmatite systems (e.g., Legg and Namateba 1982;Shearer et al 1985;Černý 1991;Jolliff et al 1992;Alfonso et al 2003). Fertile granites that are parental to mineralized pegmatites often exhibit gradual changes in fractionation indicators and levels of lithophile rare-elements enrichment with progressive evolution of its pegmatite progeny (Černý and Meintzer 1988).…”

Apparent boudinage in dykes

“…This is a common situation in the Variscan rocks of the Pyrenees, where anatectic cores of metamorphic domes are surrounded by 'perianatectic' domains with abundant pegmatites (Autran et al, 1970). However, Alfonso et al (2003) argue that the pegmatites are derived from fractionation of common parental granitoid magma. Late anastomosing shear zones cross-cut the area (Figs.…”