Mineral Systems Modeling - Opportunities and Solutions to De-Risk Green- and Brownfield Exploration

Mineral systems analysis has become an established methodology in greenfield and brownfield exploration. Understanding the mineral system more holistically enables us to de-risk exploration investment decisions and to better predict the economic potential of an area under exploration. It is only when we consider and quantify all system-critical processes over geological time, that a robust validation of a mineral system is possible, and only then is it possible to test various mineral system hypotheses. The resulting mineral system models then allow us to define the key risk factors for an effective resource assessment. Most mineralization events require a working mineral system over a specific time period, often relatively small, to enable economic metal concentrations. Here we combine 'basin modeling', the quantification of the thermal, pressure and stress evolution within the subsurface through geological time, with 'reactive transport modeling'. Modeling the fluid flow and the rock-fluid interactions allows us to define and simulate mineral systems in order to quantitatively assess their limiting factors, the impact of key uncertainties and the effectiveness of the metal concentration processes. One of the key questions to be answered in the quest for economic metal concentrations is the existence and effectiveness of the flow and/or deposit systems. Here we test this question for the Silvermines Zn-Pb-Ba deposit in Ireland. The deposit is interpreted to have formed as a result of mixing between ascending, metal bearing, hydrothermal fluids and pore fluids in the Waulsortian Limestone and it is strongly bound to a set of en-echelon normal faults. The flow analysis reveals that fault permeabilities above the Waulsortian Limestone are a key controlling factor for the fluid system to form a deposit. Modeling results show that pulsed fluid mixing leads to large amounts of carbonate dissolution, while sulfur content in the Waulsortian system does not appear to be a limiting factor to explain the massive sulfide deposits. The amount of hydrothermal pulses required to match the observed extend of the deposit can be established and a quantitative modeling of the chemical system is presented.