Data Collection and Mapping

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Exploration Technique: Data Collection and Mapping

Exploration Technique Information
Exploration Group: Field Techniques
Exploration Sub Group: Data Collection and Mapping
Parent Exploration Technique: Field Techniques
Information Provided by Technique
Lithology: Map surface geology and hydrothermal alteration. Bulk and trace element analysis of rocks, minerals, and sediments. Identify and document surface geology and mineralogy. Rapid and unambiguous identification of unknown minerals.[1]
Stratigraphic/Structural: Locates active faults in the area of interest. Map fault and fracture patterns, kinematic information
Hydrological: Can reveal whether faults are circulating hydrothermal fluids. Map surface manifestations of geothermal systems.
Thermal: Identify and delineate shallow thermal anomalies. Map surface temperature.
Data Collection and Mapping:
Data collection and mapping techniques include a broad array of methods used for collecting information about a geothermal area directly in the field. Surface mapping, shallow temperature probe surveys, and portable XRF/XRD analysis represent a valuable set of basic, cost effective tools for evaluating geothermal prospects. These methods can provide a geothermal exploration program with considerable information about a hydrothermal system prior to the application of expensive laboratory analysis or exploration drilling techniques.
Other definitions:Wikipedia Reegle

There are a number of techniques that can be applied in geothermal exploration to obtain data directly in the field, ranging from traditional geologic mapping to recently developed/refined analytical methods that can be applied outside of the laboratory setting. Basic mapping of surface lithology, hydrothermal alteration, and faults provides important information regarding the geologic setting, history of hydrothermal discharge, and the location of structures that may function as high permeability pathways for fluid circulation within the geothermal system. Shallow temperature measurements have also been used to detect deeper geothermal aquifers since the early 1980s. Recent refinements to shallow temperature probe survey methods have been used successfully to detect blind systems in the Great Basin that lack readily discernable surface manifestations. The relatively low cost of applying these techniques makes them excellent tools in the early stages of geothermal exploration, owing to the wealth of information they can provide prior to the selection of drilling targets.

Recent miniaturization of components of traditional laboratory-based analytical instruments has enabled the development of portable XRD and XRF devices that can be used in the field to enhance traditional mapping techniques. These tools can be used to analyze the bulk composition of rock, mineral, and sediment samples and to identify unknown minerals in the field, thereby assisting mappers in identifying hydrothermal alteration products that visually difficult to distinguish.[1]

Photo showing the Terra Mobile XRD system (and operator), the first commercially available portable XRD device originally manufactured by InXitu, Inc. Photo from the Olympus Corporation merchant website.

Use in Geothermal Exploration
Mapping of geologic units and faults are important exploration techniques that assist in understanding the setting of the geothermal system, identifying hydrothermal alteration, and pinpointing high permeability conduits for hydrothermal fluids. Curewitz & Karson (1997) document the common relationship between active faulting and hydrothermal systems.[2] In addition to the collection surface data, field mapping may be used to "ground truth" data collected by other methods, such as remote sensing. Water, gas, soil and rock samples are also typically collected for laboratory analysis during field investigations. Macrophotography is not a primary method for geothermal exploration; however, it can be useful during initial fieldwork to document rocks and minerals and correlate samples with lithologic units or alteration signatures identified in the field. Macrophotography can also be useful in the lab for documenting rock or core samples.

Shallow temperature probe surveys are an extremely useful and cost-effective tool for approximating the temperatures of deeper geothermal systems and mapping shallow thermal anomalies in order to find blind geothermal systems. These surveys are only effective if the geothermal system is not overlain by a cold groundwater aquifer, which will mask the temperature anomaly that could be seen in a shallow survey. Shallow temperature surveys are often conducted prior to drilling a temperature gradient borehole.

Reports of portable XRF and XRD analyses in geothermal exploration are scant, as these techniques have only been available for the past decade. Potential uses include detailed characterization of lithologic units, identification of unrecognized hydrothermal minerals, and differentiation of optically similar clays and mixed layer clays that form from distinct different weathering and hydrothermal alteration processes.

Best Practices
Advantages and ideal implementation methods are specific to the technique to be applied and to the geothermal area under investigation. Consult the individual technique pages linked in the “Related Techniques” section above for information regarding best practices for applying different data collection techniques in the field.
Potential Pitfalls
Limitations and poor implementation practices are specific to the individual technique to be applied, and may also be influenced by characteristics of the geothermal area under study. Consult the individual technique pages linked in the “Related Techniques” section above for information regarding potential pitfalls to avoid when applying different data collection techniques in the field.

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