Surface geochemistry involves collecting various materials near the earth's surface for geochemical analysis and interpretation. Geochemical dispersion patterns can be identified in samples from rock, soil, sediments (glacial, lake, stream), biological material, groundwater, and volatile substances. Exploration geochemists analyze surface geochemical data through the framework of primary and secondary dispersion. The geochemical footprints of mineral deposits can vary from a few meters to several kilometers from mineralized centers, depending on the deposit type.

Primary dispersion refers to the elemental enrichment or depletion in and around mineral deposits caused by mineral-forming processes. This dispersion occurs in rocks, where patterns of enrichment or depletion (termed halos) can exhibit systematic vertical and lateral zonation, helping to vector toward mineralized centers.

Secondary dispersion involves the redistribution of elements and materials from primary patterns in unweathered rocks due to surficial processes, including:

Each mineral deposit's surface geochemical footprint is unique due to variations in geological, geomorphological, and environmental settings. Secondary dispersion processes are influenced by erosion history, relief, climate, and regolith preservation, yet commonalities exist across deposit types due to element-mineral affinities and the predictability of element mobility under different conditions (temperature, pressure, redox potential, pH, ligand availability).

Rocks: Primary dispersion is sampled from diamond drill cores, reverse circulation chips, trench channels, and outcrops, typically weighing between 1 and 10 kg. Drill core sampling is the most representative method. Trench and outcrop sampling is done in the field.

Soils: Soil samples are common in mineral exploration, collected systematically in grids or lines over an area of interest. The type of soil profile and target horizon should align with the project's geological and environmental settings. Samples typically weigh between 0.2 and 1 kg. The regolith profile and hydrogeology influences the interpretation of soil geochemistry results.

Sediments: Stream, lake, and glacial are transported sediments. The target sediment for exploration surveys primarily depends on geomorphological setting and relief. Stream sediment sampling focuses on weathering and erosion products, with strategies to sample from active first- or second-order streams. In low-relief areas, lake sediments serve as alternatives, while glacial sediments represent transported material. Sediment samples typically exceed 10 kg, that are subsequently sieved for analysis.

Groundwater, Biogeochemistry, and Soil Volatile: These materials are used to detect buried mineralization beneath 10-100 meters of cover, assuming vertical transport of primary signals through the cover.

Surface geochemistry primarily consists of point data (x, y, z, multivariate data). Lake and stream sediment geochemistry can be linked to their catchment basins (watersheds).

Surface geochemistry is usually displayed as points on 2D maps, 3D point clouds, or gridded using geostatistical interpolants for continuous datasets. Points are symbolized by element concentration, with various shapes and sizes used for additional attributes. Logic statements can filter and classify points to highlight specific characteristics. https://www.earthbyte.org/modeling-geochemical-anomalies-of-stream-sediment-data-through-a-weighted-drainage-catchment-basin-method-for-detecting-porphyry-cu-au-mineralization/

Geochemical responses from surface samples can target ore and pathfinder elements directly or generate compositional maps to narrow areas of interest. Sediment surveys can also help predict catchment basin lithology and mineralization types based on geochemistry.

Rocks: Surface rock samples can be integrated with subsurface drill core or RC geochemical data to compose the Learning Data set and are used to define the targets in Target Generation workflows.

Sediments: Standardized sediment datasets can be linked with secondary data such as catchments, geology, satellite imagery, and various airborne geophysical data for Feature Engineering to extrapolate the response of some elements to areas where no sediment sample was collected.

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