Chemical Diagenesis of the Devonian Carbonate Rock in the Fankou Lead -Zinc Mine Area

Key words: 
• diagenesis /
• dissolved - solidification /
• carbonate rock /
• Fankou

Abstract: The multiple - stage diagenesis was revealed by the cathodoluminescence of carbonate rock samples.The minerals pre-cipitated in shallow - burial condition where the primary diagenesis occured are higha in a Mn content with weak lumines-cence, which resulted from the drop of Eh and pH values due to the decomposition of organic substances.With furtherfalling of the Eh and pHvalues, the increase of Fe 2+ contained in the minerals quenched the luminescence.Being in a deep -burialcondition, the pHvalue was controlled by the equilibrium between carbonate minerals and water, so the environmentis alkalescent.The condition is favourable to the formation of M n (Ⅱ ) cation and contrary to Fe (Ⅱ ) cation.As a result,this precipitated minerals have a bright luminousness.The carbon and oxygen isotope compositions of the whole rocks deviated from the range of marine environment butweve close to that of fresh - water diagenetic environment.Diagenetic solution based on the Sr / Ca ratio in the minerals wasanalogous to that of fresh - water mixed with less than 10 % marine - water.This solution made the minerals in lime - mudsediments dissolved and brougt about dissolved - reprecipitatlon a dynamic equilibrium with the increase of saturation.Baced on the studies above, the authors suggested “ dissolved - solidification ” is a new diagenetic pattem of lime - mudsediments solidified in fresh - water by way of dissolved - reprecipitation, which made the new minerals arranged inseparably.