HYDRODYNAMIC CONDITIONS OF SOLUTIONS MIXING IN FORMATION OF CROSS-CUTTING ORE VEINS IN LAYERED ROCK SEQUENCES

Selective ore localization at the sites of intersection of ''favorable '' rock units by cross-cutting veins is often observed at vein-type de posits in layered rock sequences. Lithological control, i.e., chemical interaction of ore-bearing solutions with favorable host media, is su pposed to be a predominant cause of selective ore localization. The co ncept of ''host media'' includes the host rock mineral matrix and form ation solution. Correspondingly, two main mechanisms of lithological c ontrol can take place: the interaction of ore-hearing solutions with t he host rock mineral matrix and/or with its formation solution. The la tter is the most probable explanation in the case where selective loca lization of ore in veins is combined with a weak metasomatic alteratio n of the enclosing rocks. Mixing of the fault and formation solutions in the ore-controlling channel is a necessary prerequisite for the ori gin of ore veins via the chemical interaction of solutions. The idea o f mixing of chemically different solutions as a cause of hydrothermal ore deposition was proposed hv a number of authors long ago (Betekhtin , 1953; Smirnov, 1976; etc.). However, an application of this hypothes is to interpretation of observations at specific ore deposits was halt ed by a lack of the adequate concepts on the hydrodynamic mechanism of the process. The results of computer simulation of hydrodynamic inter action between fault and formation solutions obtained for the represen tative model of horizontal layer crossed by a vertical fault, partiall y fill up this gap and are outlined in this paper. The considered mode l explores the key features of the fault and formation solutions mixin g, including as a particular the previously examined model of solution s ''self-mixing'' (Barsukov, Laverov, and Pek, 1977; Barsukov and Pek, 1980). For this last model, the physicochemical simulation of ''solut ion + rock'' and ''solution + solution'' interactions was carried out (Barsukov and Borisov, 1988, 1989, 1990). However, the results obtaine d are also pertinent to the more general case examined in this paper. Joint consideration of these results (obtained from physicochemical an d hydrodynamic modeling) suggests that different combinations of hydro dynamic and physicochemical conditions at the site of mixing of format ion and fault solutions must lead to development of specific patterns in spatial distribution of ore mineralization and of wall rock metasom atites. Such relations offer new possibilities for genetic reconstruct ion of the ore-forming systems and, in particular, for revealing the o re matter sources and proportions of the ore-bearing and ore-precipita ting solutions mixing.