Secuencia de emplazamiento, alteración hidrotermal y metamorfismo en el Complejo Intrusivo de Jörn, distrito minero de Skellefte, norte de Suecia

Abstract

The Skellefte district is one of the most important mining districts in Sweden, located in an early Proterozoic (1.90-1.87Ga) volcanic arc province in the Baltic Shield, northern Sweden. The district consists of a complex volcanosedimentary succession formed by submarine, mainly felsic, volcanic rocks named Skellefte Group, overlain by a subaerial, felsic volcanic succession named Arvidsjaur Group and shallow- to deep-marine sedimentary rocks known as Vargfors Group (Allen et al., 1996). The Jörn Granitoid Complex (JGC) crops out at the northern boundary of the Skellefte district, and is constituted by several intrusions ranging in composition from gabbro to granite. Some features of the JGC suggest that it is comagmatic with the volcanic rocks of the Skellefte and Arvidsjaur Group. Our recent study has revealed that earlier intrusives in the complex (GI) have significant geochemical differences with the rest of plutonic rocks in the complex (GII to GIV). Crystallization of GI was followed by intense hydrothermal alteration and late, regional contact metamorphism that do not affect the later GII to GIV facies. This sequence in time, together with the chemical contrasts between the successive Jörn facies, suggests that a significant time gap lasted between the emplacement of GI and the later plutonic rocks in the Jörn complex. This is probably relevant to the geological history and ore research in the district, in that a major change occurred between GI and the rest of the JGC facies, involving changes in the geochemical character of magmatism and coeval thermal activity