Seawater Alteration of Early Precambrian (Archean) Volcanic Rock and Exploration Criteria for Stratiform Gold Deposits, Porcupine Camp, Abitibi Greenstone Belt, Northeastern Ontario

Abstract

<p>Regionally distributed, low temperature (<250°C), synvolcanic interaction between seawater and Early Precambrian (Archean) tholeiitic and komatiitic volcanic rocks in the Timmins area is characterized by relict palagonitization textures, elevated abundances of K₂O, Rb, Li, Ba, B, H₂O and CO₂ in the altered flows, and localized, intensely altered chlorite and carbonate-rich zones which occur throughout the tholeiitic and komatiitic volcanic stratigraphy as discordant and stratabound zones. These localized alteration zones formed at the seawater/seafloor interface and in a subseafloor volcanic environment. Only the alteration zones which developed in the seafloor environment are associated with local accumulations of felsic volcanic rock and exhalative, auriferous, cherty dolomites. Subsequent to the low temperature, seawater alteration of the flows, the volcanic pile was metamorphosed to greenschist facies.</p> <p>Gold is leached from the volcanic rock during the most intense stages of the carbonate alteration. There is no significant difference between the gold content of komatiitic and tholeiitic flows.</p> <p>Altered magnesium tholeiitic basalts which are spatially associated with auriferous, cherty dolomite-type mineralization are enriched in Li (> 30 ppm), B (> 30 ppm), Sb (> 0.35 ppm), Au (> 5 ppb), and As (> 70 ppm) and are depleted in Cu (< 70 ppm), with respect to altered basalts not associated with such gold mineralization. Ore-related, altered komatiitic flows can be screened only using Au (>5 ppb) and As (>70 ppm).</p>