Alteration zonation Loma Blanca kaolin deposit, Los Menucos, R¨ªo Negro Province, Argentina

MAIZA PEDRO; MARFIL SILVINA; MONTECCHIARI NICOLAS

Castellaneta Marina (Italia)

Conferencia; XIV International Clay Conference; 2009

AIPEA

Loma Blanca is a kaolin deposit situated 70 km NW of Los Menucos (R¨ªo Negro Province ¨C Argentina). The parent rock is a lower Triassic andesite (Vera Formation ,Los Menucos Group). Hayase et al. (1974) proposed a concentric zonation model.  From the parent rock outward, three different alteration patterns were recognized. Zone 1. with sericite, chlorite and montmorillonite. Zone 2 with kaolinite and dickite.  Zone 3 with dickite, pyrophyllite and alunite-natroalunite and  zone 4 with quartz, disseminated sulfides and diaspore. The relation between the chemical composition of major, minor and trace elements and the mineralogical alteration zonation was evaluated to confirm the genesis of the deposit. Fe2O3, CaO, Na2O, y K2O contents decrease from zone 1 to zone 3 whereas Al2O3 and LOI increase in the kaolinite-alunite zone. In alunite composition sodium prevails to potassium. High Ba, Sr, V y Zr contents were observed principally in zones 2 and 3.  Co, Ni, Cu, Zn y Rb are more common in zone 1.  LREE are more abundant than HREE in zones 2 and 3. ¦Ä 18O in kaolinites range from 10.8 to 13.2 %0 and ¦ÄD from -83 to -85 %0 The mineralogical association (dickite-alunite-pyrophyllite-dispore), the alteration zonation pattern, laterally concentric, the geochemistry of the trace elements, the relation between LREE and HREE and the low ¦Ä18O values, suggest that ¡°Loma Blanca deposit¡± was formed by hydrotermal proceses. Hayase, K. and Maiza, P. (1974). G¨¦nesis del yacimiento de caol¨ªn de mina Loma Blanca, Los Menucos, Provincia de R¨ªo Negro, Rep¨²blica Argentina. V Congreso Geol¨®gico Argentino. Actas. 139-151.