Porphyry or Not Porphyry: That´s Not The Only Question

Abstract

Tapajós (PA) and Alta Floresta (MT) gold areas form one large (1,900 km long and 280 km wide) Paleoproterozoic gold province named Tapajós – Alta Floresta Gold Province (TAFGP). Gold deposits from the TAFPG are divided into two major groups: (1) Epithermal and pluton-related high grade quartz vein deposits ±(Zn-Pb-Cu-Fe) with restricted sericite, chorite and carbonate alteration; and (2) Low grade disseminated deposits ±(Ag-Bi-Te-Pb-Zn) with “phyllic” fault-controlled alteration (muscovite-quartz-pyrite) and strong to moderate silicification. Early k-feldspar alteration is pervasive and not related to gold grades. TAFGP deposits are not porphyry-type or intrusion related strictu sensu gold deposits. Additionally, TAFGP gold deposits are not related to subdution zones. Seismic thomography revealed that the TAFGP sits over a rifted SCLM keel (Amazon archean craton). TAFGP gold deposits represent a new type of gold mineralization related to intracratonic A-type volcanic-subvolcanic-plutonic system generated by large underplate-plume