Porção sul do batólito Serra da Providência e sua inserção no panorama metalogênico da Província Estanífera de Rondônia: percepções sobre uma possível recorrência das mineralizações estaníferas

Abstract

The Serra da Providência Suite is located in the southwest portion of the Amazonian Craton and corresponds to an expressive amount of anorogenic magmatism related to post-colision moment of the Rondônia-Juruena or Ouro Preto orogeny (1.67 to 1.63 Ga). This suite assembles hornblende-biotite syenogranites and biotite syenogranites with rapakivi textures, charnockites, mangerites and related mafic rocks. The granitoids vary from medium-grained equigranular to coarse-grained porfiritic texture, with from isotrope to foliated fabric. The U-Pb ages in zircons are between 1,606 and 1,532 Ma. The present work is based in fieldwork surveys and petrographic, litogeochemistry and geochronological studies (Sm-Nd in bulk rock and U-Pb/Lu-Hf in zircon by LA-ICP-MS) in the granitic facies that conform the southern portion of the Serra da Providência Batolite. The main objective of this work is to propose a geological evolution of the southern portion of the Serra da Providência Batolite, relating its role in the tin metallogeny scenery of Rondônia, possibly exposing a recurrence of tin mineralizations along the geologic time. In this context, the Serra da Providencia Suite is the first tin magmatic pulse mineralized and possibly the precursor of this process. This work identified biotite granophyres, with concord age of 1,577±12 Ma, containing <1% cassiterite contents, and also quartz-sericite greisens containing cassiterite and with 1,638 ppm of tin content, and massive hematite bodies with average content of 537 ppm of tin. Samples of the mineralized biotite granophyre have positive &#400;Hf values indicating that there was only a mafic magma input, originated from the mantle melting, resulting in the crystallization of that rock. The distinguished compositional gap between the viborgite/pyterlite and the granophyric granites samples, in several geochemical diagrams, confirms the hypothesis that magmas of different sources probably crystallized through the fractional crystallization process. Nine geochronological U-Pb data confirmed that the magmatism of the southern portion of the Serra da Providência Batolite crystallized in the ages between 1,587 and 1,576 Ma, within the calculated deviation limit of ±16 Ma. Therefore, it is suggested that the main mechanism of tin input in the magma that originated the Serra da Providência Suite derives from a mafic magma with TDM ages between 1.93 and 2.20 Ga, formed by the mantle melting. It is also suggested that there is still a parental tin reservoir of tin for the Rondônia Tin Province related to the continental crust prior to the sub outcropping Jamari Complex (2.28 to 2.37 Ga), given the fact that in this region of the Amazonian Craton there are no register of other rocks older than 1.76 Ga