Abstract
In the northeastern Ladoga region, the Riphean agate-bearing volcanic rocks of the Priozersk Formation are composed of basaltic lavas and lava breccias. Agates occur in the upper lava flow and in overlying conglomerate of the Salmi Formation. By their patterns, the agate amygdules correspond to concentrically zoned varieties, while agate veinlets have a vague pattern. Microstructures of agates are diverse, We backspace we including quite peculiar ones. Agates with enveloping zoning (the main structural type) were formed in closed cavities, whereas agate veinlets usually occurred in open connecting fissures and were replaced by calcite at the late stage of mineral formation. The unusual absence of quartzine suggests a low SiO2 concentration in the agate-forming solutions and/or a low pH value.
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Original Russian Text © Yu.S. Polekhovsky, Yu.O. Punin, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, No. 3, pp. 119–123.
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Polekhovsky, Y.S., Punin, Y.O. Agate mineralization in basaltoids of the northeastern Ladoga region, South Karelia. Geol. Ore Deposits 50, 642–646 (2008). https://doi.org/10.1134/S1075701508070167
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DOI: https://doi.org/10.1134/S1075701508070167