Understanding the mineral systems, geology and structural architecture is critical in helping narrow the exploration search window for targeting mineralisation. Data is a fundamental component of this process. Modern exploration programs typically involve a vast array of multi-disciplinary datasets at a range of scales. The application of GIS and 3D modelling systems allow these datasets to be interpreted in a common platform and space, enabling improved understanding and exploration success.
The Zaraagiin Tal Project is a recent example of how this integrative approach can be applied to improve mineral system understandings and exploration targeting. The project lies approximately 160 km southwest of Ulaanbaatar in the Tuv province of Mongolia and is interpreted as an epithermal, low sulphidation gold and silver deposit. Exploration is advanced, with numerous datasets collected across the deposit, inclusive of data from geological mapping, magnetics, gravity, seismic, induced polarity (IP), drilling and alteration assemblage investigations from drilling and outcrop. SRK’s work consisted of several phases of data interpretation and field-based investigations to better understand the underlying mineral system and mineralisation controls to assist with drill targeting and upgrading the Mongolian-standard resource to a Mineral Resource estimated under the guidelines of the JORC Code.
Preliminary stages of this work consisted of initial data integration in GIS and interpretations of geophysical datasets (magnetics and gravity) to define the regional structural architecture. This was coupled with the acquisition of ASTER and Landsat satellite data to help identify alteration patterns identified as being associated with mineralisation.
Following preliminary interpretations, field mapping was undertaken to better define the local structural architecture and controls on gold mineralisation as well as ground-truth the broader ASTER and geophysical interpretations for targeting. A dominant north-northwest orientation to quartz veining was defined with a secondary west-northwest orientation observed. Observed quartz veins were typically milky white in appearance, with bladed textures also commonly observed. Veins were also observed forming as complex stockworks and quartz breccia. Observed alteration signatures included strong siliceous alteration with zones of sericite, muscovite, illite and local kaolinite, consistent with mineralised drill intercepts defined in previous alteration studies.
3D structural and lithological modelling in Leapfrog™ was conducted, enabling integration of field-based observations with the broader project datasets and GIS interpretations A clear northwest-trending structural orientation was defined based on the 3D interpretations of the drilling and seismic datasets, consistent with observations from magnetic datasets and field mapping. In addition, a major northwest-trending fault was identified from seismic data, with significant displacements (100 m) observed and interpreted to have developed as a complex dextral strike-slip fault system.
Mineralisation modelling was then conducted to better understand the underlying lithological and structural controls. Mineralisation was observed to correlate with the mapped vein orientations and shows a close spatial relationship with the major northwest striking dextral fault system (Figure 1). From this, it was possible to define potential mineralisation extensions along strike and down dip for immediate infill drill targeting. In addition, the observation of this underlying northwest orientation was criterial to the broader mineralising system, acting as a favourable dilational orientation for fluid flow, and with mineralised quartz veins forming in a position of synthetic Riedel shears and tension gashes to a broader regional dextral system.
The exploration targeting based on these underlying mineralisation system controls helped expand the current resource extents as well as delineate several additional targets in the broader licence area. Targeting integrated several key elements, including structural dilation sites, favourable alteration signatures from ASTER and favourable brittle host rock lithologies that promote fluid penetration during deformation. Exploration is ongoing within the project area, with additional mineralisation identified from recent drilling.
While there is always a degree of inherent risk and uncertainty associated with exploration effort, this case study highlights that developing knowledge of the underlying geology and broader mineral system is fundamental to reducing some of these risks. Platforms such as GIS and 3D modelling are enabling better interpretation of geology in increasingly more complex geological terrains and helping significant mineral discoveries to be made.
