GOLD IN AND AROUND GRANITE: THE STRUCTURAL LINK (Invited Presentation)

A permanent doubt still exists regarding the role of granitic intrusion in the mineralizing process allowing the formation of mesothermal gold mineralizations. This led to the application of several classical models such as “orogenic”, “Intrusion related”, “Intrusion-hosted” and let subsisting a general confusion in defining the gold-bearing lode deposit occurring within middle crust continental and orogenic domains. The frequent questions and uncertainties remaining are the following:

• Is there a magmatic contribution in the mineralizing fluid?
• Is there a mechanical role of granite emplacement in the development of the mineralized system?
• Is there only a thermal role of granite in creating circulation of hot fluids, leaching and gold transport?
• What is the respective role of host rocks lithology and/or granite in providing the metallic source?

A lot of methodologies have been intensively used in order to track the source, the nature, the mode of circulation and the distribution of the mineralized fluids hoping to definitively answer to the above questions. The results are often unsatisfying and the duality between “intrusion-related” and “orogenic” models remains. As an example, the recurrent question about the role of magmatic, metamorphic or meteoric fluids is at the center of the debate between the two classical Intrusion-related vs orogenic deposits.

In this contribution, it is proposed to present several case studies of lode mineralization (mainly gold-bearing) in which specific relationships with surrounding granite will be established and discussed. The purpose is to demonstrate that establishing that granite and mineralization were formed under the control of a single structural context involves that both features were coeval and continuous in time and space. This “structural link” thus represents a convincing argument at least demonstrating that granite and mineralization were intimately related and maybe associated within a transitional process between late magmatic stages and purely hydrothermal ones.