Genetic relationship between greisenization and Sn-W mineralizations in vein and greisen deposits: Insights from the Panasqueira deposit (Portugal)

The W-Sn Panasqueira ore deposit is a magmatic-hydrothermal system, which includes a high grade quartz-vein type mineralization and underneath disseminated greisen-type mineralization located in the upper part of a two-mica granite. We investigate genetic and chronological relationships between greisenization of the Panasqueira granite and the formation of ore-bearing quartz veins by monitoring major and trace elements variations in quartz-muscovite assemblages composing the two-mica granite, greisen and ore-bearing quartz veins. Greisen is marked by an overall depletion in Mg, Ti, Ca, Na, Ba, Sr, REE and enrichment in Fe, Li, Rb, Cs, Sn, W that reflect the breakdown of feldspars and biotite and implication of W-Sn-bearing fluids during greisenization. Muscovite from greisen and mineralized quartz veins are enriched in granophile elements (F, Rb, Cs, Li, Sn, W and Zn) compared to magmatic muscovite from the two-mica granite. Trace elements contents in quartz depict evolutionary trends with progressive enrichment in Ge and B and depletion in Al, Ti and Li between magmatic and hydrothermal quartz that emphasize the progressive evolution and cooling of the magmatic-hydrothermal system of Panasqueira. Multivariate statistical approach applied on quartz and muscovite data demonstrates similarities in composition between quartz and muscovite from greisen with those composing ore-bearing quartz veins. These similarities suggest that greisenization and the formation of mineralized veins result from the same hydrothermal event and derived from the same source of hydrothermal fluids. Apatite from greisen and quartz vein yielded respectively U-Pb ages of 29210Ma and 295 +/- 5Ma confirming that greisenization and the formation of mineralized veins occurred roughly at the same time. These ages also overlap with the cooling age of the Panasqueira granite (296 +/- 4Ma), indicating a temporal and genetic link between greisenization, W-Sn mineralization and the granite crystallization. Temperatures of the magmatic-hydrothermal system constrained by Ti-in quartz thermometry depicts a cooling trend from magmatic quartz of granite (700-600 degrees C) to hydrothermal quartz of greisen (500-400 degrees C) and veins (450-350 degrees C). These results provide evidences that greisenization and the formation of W-Sn bearing quartz veins occurred at the magmatic-hydrothermal transition, during which orthomagmatic fluids rich in volatils, incompatible elements and metals (W and Sn) were exsolved at the final stage of solidification of the Panasqueira two-mica granite. Le gisement a W-Sn de Panasqueira (Portugal) est un systeme magmatique-hydrothermal de type veine et greisen dont la mineralisation se presente principalement sous la forme d'un reseau dense de veines a quartz-wolframite. Ce gisement comprend egalement des mineralisations disseminees a faibles teneurs au sein d'un apex granitique greisenise. Cette etude vise a contraindre les relations genetiques et chronologiques entre la greisenisation du granite de Panasqueira et la formation des veines a W-Sn en s'appuyant sur la composition geochimique des assemblages a quartz-muscovite composant le granite, le greisen et les veines mineralisees de Panasqueira. Le greisen se caracterise par un appauvrissement en Mg, Ti, Ca, Na, Ba, Sr, REE et un enrichissement en Fe, Li, Rb, Cs, Sn, W refletant (i) l'alteration des feldspaths et de la biotite et (ii) l'implication des fluides porteurs de la mineralisation a W-Sn lors de la greisenisation. La muscovite composant le greisen ainsi que les veines de quartz mineralisees sont enrichies en elements granophiles (F, Rb, Cs, Li, Sn, W et Zn) par rapport a la muscovite magmatique composant le granite. La composition en elements trace des differentes generations de quartz magmatiques et hydrothermaux montre un enrichissement progressif en Ge et B et un appauvrissement en Al, Ti et Li entre quartz magmatiques et hydrothermaux. L'application d'approches statistiques multivariees demontre que les compositions geochimiques des quartz et des muscovites composant le greisen et les veines mineralisees sont similaires. Ces similarites suggerent que la greisenisation et la formation des veines mineralisees de Panasqueira resultent d'un meme evenement hydrothermal et impliquent la meme source de fluides. Les apatites presentes au sein du greisen et des veines mineralisees se caracterisent respectivement par des ages U-Pb de 292 +/- 10Ma et 295 +/- 5Ma confirmant que la greisenisation est contemporaine a la formation de veines mineralisees. Ces ages sont egalement compatibles avec l'age de refroidissement du granite (296 +/- 4Ma) indiquant un lien temporel et genetique entre la greisenisation, la mineralisation a W-Sn et la cristallisation du granite de Panasqueira. Les temperatures du systeme magmatique-hydrothermal contraintes a partir du geothermometre TitaniQ (Ti-Quartz) montrent un refroidissement progressif des quartz magmatiques du granite (700-600 degrees C) vers les quartz hydrothermaux composant le greisen (500-400 degrees C) et les veines mineralisees (450-350 degrees C). Ces resultats indiquent que la greisenisation et la formation des veines a W-Sn de Panasqueira se sont produites lors de la transition magmatique-hydrothermale, au cours de laquelle des fluides d'origine magmatique riches en volatils, en elements incompatibles et en metaux (W et Sn) ont ete expulses lors de la cristallisation du granite de Panasqueira.

Automated summary

The W-Sn Panasqueira ore deposit is a magmatic-hydrothermal system, with high grade quartz-vein type mineralization and disseminated greisen-type mineralization, where similar compositions suggest a genetic link between greisenization and the mineralized veins formation, occurring during the magmatic-hydrothermal transition at the final stage of solidification of the granite. The greisen is marked by depletion in Mg, Ti, Ca, Na, Ba, Sr, REE and enrichment in Fe, Li, Rb, Cs, Sn, W, reflecting the impact of W-Sn-bearing fluids during greisenization. The U-Pb ages of apatite from greisen and quartz vein confirm the simultaneous occurrence of greisenization and mineralized veins formation, indicating a temporal and genetic link between greisenization, W-Sn mineralization and granite crystallization.