Pegmatites of Eight Mile Park, Fremont County, Colorado

Origin of rhythmic layering in the Calamity Peak satellite pluton of the Harney Peak Granite, South Dakota: The role of boron☆

The co-occurrence, at the thin section scale, of the three anhydrous Li-aluminosilicates spodumene, petalite and eucryptite, is not a common feature. Such an association occurs in some aplite–pegmatite dykes of the Covas de Barroso district, northern Portugal. We describe their mutual relationships: where spodumene is an early magmatic phase, petalite precipitates directly fr om a late orthomagmatic fluid, the spodumene remaining metastably, whereas eucryptite is obviously hydrothermal and secondary. Replacement of the primary Li-minerals is the rule, but is diversified and selective: spodumene is mainly replaced by albite an d muscovite, petalite by K-feldspar and eucryptite. Muscovite is widespread, and the late hydrothermal paragenesis is dominated by quartz associated with various mixtures of phosphates. The assemblage eucryptite, K-feldspar and albite is obviously in chemical disequilibrium with the early phases. The compositional evolution of the hydrothermal fluids (Na, K, Li) is tentativel y bracketed. There is disequilibrium among thermodynamically conflicting mineral phases in terms of pressure, temperature and fluid:rock ratio, in a mobile and partly open system. A genetic affiliation of the Li-enriched pegmatites with the nearby two-m ica granites is difficult to prove. The tectonically controled intrusion of biotite granites to the east of the pegmatite belt woul d seem to be responsible of the drop in pressure that accounts for the spodumene–petalite transition and the development of the widespread replacement by feldspars, not present in the western part of the belt.

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SPODUMENE – PETALITE – EUCRYPTITE: MUTUAL RELATIONSHIPS AND PATTERN OF ALTERATION IN Li-RICH APLITE–PEGMATITE DYKES FROM NORTHERN PORTUGAL

The geochemistry of K-feldspar for K, P, Sr, Ba, Rb, Cs, Ga, and of muscovite for the same elements plus Nb and Ta, was used for proving the parental relationships of S-type granites and LCT (Li, Cs, Ta) rare-element pegmatites in the southernmost pegmatitic field of the Pampean pegmatite province in Argentina. The variation of K/Rb-Cs, K/Cs-Rb, K/Rb-Rb/Sr, K/Rb-Ba in K-feldspar from the granites and pegmatites show that they form an association with the evolutional sequence: granites → barren- to transitional pegmatites → beryl type, beryl-columbite-phosphate pegmatites → complex type of spodumene subtype pegmatites → albite-spodumene type → albite type pegmatites. This sequence reflects the regional distribution of the different magmatic units. The Ta-Cs diagram for muscovite reveals that none of the studied pegmatites exceed the threshold established in previous studies for being considered with important tantalum oxide mineralization. The granites and pegmatites constitute a rare-element pegmatitic field in which different magmatic units form a continuous fractionation trend, extended from the less evolved granitic facies to the most geochemically specialized pegmatites

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1751-3928.2009.00100.x

Geochemistry of K-feldspar and Muscovite in Rare-element Pegmatites and Granites from the Totoral Pegmatite Field, San Luis, Argentina

A preliminary report is presented on the paragenesis of the Varutrask pegmatite, situated about 10 km. from Skelleftea, in Sweden. Three main stages can be distinguished ( a ) An epimagmatic-pegmatitoid stage during which the primary zonal development of the pegmatite body into border zone, wall zone, intermediate zones, and core was accomplished; ( b ) a hydrothermal replacement stage, divisible into a high temperature phase with a Li-replacement unit and a Cs-replacement unit, and a lower temperature phase with a cleavelandite replacement unit and a feebly developed fluorite unit ( c ) a final stage of supergene alteration. The age of the pegmatite lies between 1650 and 1800 million years.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/08B83F986DB4357DBA7E816FD5178F74/S0016756800067315a.pdf/div-class-title-the-paragenesis-of-the-varutrask-pegmatite-div.pdf

Pegmatites of Eight Mile Park, Fremont County, Colorado

Citations

Origin of rhythmic layering in the Calamity Peak satellite pluton of the Harney Peak Granite, South Dakota: The role of boron☆

SPODUMENE – PETALITE – EUCRYPTITE: MUTUAL RELATIONSHIPS AND PATTERN OF ALTERATION IN Li-RICH APLITE–PEGMATITE DYKES FROM NORTHERN PORTUGAL

Geochemistry of K-feldspar and Muscovite in Rare-element Pegmatites and Granites from the Totoral Pegmatite Field, San Luis, Argentina

The Paragenesis of the Varuträsk Pegmatite

Zoning in pegmatite districts