Fluid pressure variations in relation to multistage deformation and uplift; a fluid inclusion study of Au quartz veins

Using a detailed characterization of quartz microdomains and related fluid inclusions, and the determination of composition- molar volumes for each stage of fluid migration, a reconstruction of the changes in fluid P throughout crack healing or filling has been carried out for quartz veins in the Montagne Noire, French Massif Central. The estimated conditions of an early microfissuring-healing event affecting milky quartz are: minimal P (homogenization P, P (sub h) ) 260-450 MPa, maximal and minimal trapping P assuming a T range of 350-400 degrees C, 400-450 and 260-290 MPa, respectively, at Malabau, and 250 and 150 MPa (at 300- 350 degrees C) at Cabrespine; maximal depth in the 10-19 km range depending on the hypotheses. This stage follows arsenopyrite deposition but precedes later microfissuring associated with a Au- Bi-Cu stage which occurred under much lower P-T conditions.