Geochemistry refers to a broad area of Earth Sciences that utilizes analytical chemistry techniques at various scales to quantifiably measure and map elemental composition of earth materials. For our purposes, drill core geochemistry refers to the chemical data collected on diamond drill core.

Geochemistry, assays and lithogeochemistry may mean different things to different people, the table below is how we think about these terms:

Exploration geochemists use the framework of primary and secondary dispersion to investigate the geochemical signature of mineral deposits. Primary dispersion refers to elemental enrichment and / or depletion in and around epigenetic and syngenetic mineral deposits that were caused by mineral forming processes.

Primary dispersion occurs in the rocks sampled by diamond drill cores. The patterns of elemental enrichment and / or depletion, termed halos, commonly exhibit systematic vertical and lateral zonation that can be used to vector to mineralized centers. In epigenetic mineral deposits, the complex interactions between protolith (host rock) composition, fluid flow pathways, fluid composition, and subsequent oxidation / weathering influences the drill core geochemical composition.

There are, however, commonalities between deposit types and environments due to element-mineral affinities and the predictability of element mobility under different conditions (fluid-rock ratio, temperature, pressure, Eh, pH, ligand activity). Depending on the deposit type, the primary and secondary geochemical footprints can span distances from a few meters to several kilometers from the mineralized center.

Data collection begins with a drill rig positioned over a target location, drilling into the bedrock to extract drill core in approximately 10-foot runs. The rock is placed into boxes and delivered to the geology team for detailed logging. The core is sampled at regular intervals then cut in half, with half of the core sent to a lab for geochemical analysis and the other preserved on-site for future observations. At the lab, the samples are dried, crushed, split, pulverized, and dissolved before being assayed according to the method selected by the client. Quality Assurance and Quality Control programs are the foundation of accurate and trustworthy geochemical data and should test for representativeness, accuracy (bias), and precision at each stage of sample mass reduction. Assay results are provided back to the client as a CSV file database import.

Drill core geochemistry is interval based with sample ID’s and results assigned a “from” and “to” value down the hole that correspond to the start and end of the cut material that was sampled. Individual assays can also be converted to points by de-surveying the drill hole to extract midpoint coordinates of each sample range. It is common practice to composite initial assay lengths for estimation purposes.

Exploratory data analysis of drill core geochemical data can be done in uni-, bi-. and multi-variate space. Results are displayed down the drill string in 3D visualization packages such as Geoscience Analysts and LeapFrog. A plethora of continuous and categorized color schemes exist that can be used to identify high and low values or communicate specific concentrations of interests in assay results. Interpolants such as iso shells can be quickly generated to assess spatial continuity and volumes. De-surveyed results can be projected to the surface to display in GIS software.

The geochemical response from drill cores can be used to directly target ore and pathfinder elements. The data can be used to generate specific compositional maps and 3D domains to help vector to higher grade and additional mineralization, as well as characterize host rocks. Further, when the metal of interest is analysed, the data serves as a way to quantify the location and quantity of mineralization.

Rocks: Drill core geochemistry can be integrated with surface outcrop or trench data to compose the Learning Data set from which target elements, typically ore element assays, and thresholds are selected for the Target Generation workflow.

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