Description

Location: The Martin Hotel, 94 W. Railroad St.

Contact: Kris Alvarez: krisalvarez48@gmail.com

Please join us for our Winnemucca GSN November Meeting on

Wednesday, November 8, 2023

 The Martin, 94 W. Railroad St., Winnemucca, NV

 Food and Drinks at 6 pm; Talk at 7 pm

 Speaker:  Joseph Laravie, Geologist, Great Basin GIS

 Talk:  The Geo-Physical Continuum: An Introduction to Mineral Exploration Geophysics for Geologists

FOOD AND BEER SPONSOR:  PREMIER DRILLING CO.

Please contact Kris Alvarez at kalvarez@i80gold.com, phone: 775-770-4615; or Eli Witte at witteeli9@gmail.com

ABSTRACT:

Geologists describe rocks using lithology, alteration, color, texture, and structure, among other things. Geological observations are limited to the earth’s surface and drill holes. Interpretations of geology far from these observation areas are necessarily speculative. Geophysical techniques can observe areas far from the surface and between drill holes, but do not detect these same geological characteristics. They can “see” only bulk physical properties, such as density, electrical resistivity, seismic velocity, and others. Geophysical techniques are also limited by “poor vision”, including limited detection distance, sensitivity, resolution, and masking.

Density is the most easily understood physical property. It is controlled primarily by mineralogy, pore space, and pore fluid. Denser minerals, less pore space, and existence of a pore fluid all contribute to higher density. Density is detectable using gravity surveys, in which minute variations in earth’s force of gravity are measured at the earth’s surface, in drill holes, or from aircraft, and interpreted to estimate earth’s density in 2 or 3 dimensions over a limited region. Gravity surveys are typically used to estimate sedimentary basin thickness, or detect the presence of large masses of differing density. Local gravity surveys can detect the presence of volcanogenic massive sulfide (VMS) deposits due to the higher density of sulfide minerals relative to host rocks.

Electrical resistivity is the resistance of earth materials to the flow of electricity, principally alternating current within the audio-frequency range. Resistivity is controlled by mineralogy, mineral spatial relationships, porosity, and pore fluid types. Metallic-luster minerals, clay minerals, increased pore space, and conductive (salty) pore fluids decrease resistivity. Resistivity is detectable using several different geophysical techniques that involve injecting electrical current or magnetic fields into the earth. Resistivity surveys can detect VMS deposits, and can also be used to map a wide range of resistivity in three dimensions over entire project areas.

Chargeability is the ability of the earth to briefly store an electrical charge. This physical property is caused by disseminated metallic-luster minerals, The magnitude of the effect is more-or-less proportional to their surface area, thus finer grain size tends to maximize the effect. Chargeability is detectable using “Induced Polarization” (IP) surveys that inject electrical current into the earth. IP surveys are most commonly used in the exploration for porphyry copper deposits, but can also used in other settings where sulfides are important.

Magnetic Susceptibility is a property whereby a non-magnetic material can locally modify a vector magnetic field (normally Earth’s field) that it is immersed in. This has the effect of causing local variations in Earth’s field. Magnetite is the primary mineral that shows this effect. Pyrrhotite also possesses a weaker version of this physical property.

Magnetic Remanence is the physical property whereby minerals are naturally magnetic and possess a local magnetic field, with north and south poles, the same as a household bar magnet. This local magnetic field combines with (adds to) Earth’s dipole vector field creating local variations. These local effects can add to or subtract from the anomalies created by magnetic susceptibility. Both magnetite and pyrrhotite can possess magnetic remanence, but it can be strong, weak, or undetectable. The combined effect of both magnetic susceptibility and remanence are measured using hand-held or airborne magnetometers, Magnetic surveys are extremely useful in the search for magnetic iron ore, and also for general geological mapping in rocks that have only low concentrations of magnetite.

Seismic Velocity is the speed of sound within the earth. While the speed can be measured directly, discontinuities and boundaries between layers of different seismic velocity are easier and more commonly detectable. This effect is detectable by sequentially injecting sound energy into the earth in an array of locations, and detecting the response at the earth’s surface at many points in their vicinity. Seismic surveys are highly developed in the petroleum industry, but are less common in mineral exploration, due to high cost and other factors.

The earth’s surface emits natural gamma rays due to the presence of uranium, thorium and potassium. Each element (daughter products for U and Th) emit gamma rays of different energies. These can be detected and differentiated by gamma-ray spectrometers, some of which are small hand-held instruments, or larger more sensitive systems for airborne surveys. The most common use is as down-hole instruments in uranium exploration and development. Natural gamma rays penetrate only a very short distance (several feet) in soil, less in rock, severely limiting their 3-D utility.

 

Details

05/11/2022 18:00:0005/11/2022 20:30:00America/Los_AngelesGSN Winnemucca Chapter Meeting – November 8, 2023

Please join us for our Winnemucca GSN November Meeting on

Wednesday, November 8, 2023

 The Martin, 94 W. Railroad St., Winnemucca, NV

 Food and Drinks at 6 pm; Talk at 7 pm

 Speaker:  Joseph Laravie, Geologist, Great Basin GIS

 Talk:  The Geo-Physical Continuum: An Introduction to Mineral Exploration Geophysics for Geologists

FOOD AND BEER SPONSOR:  PREMIER DRILLING CO.

Please contact Kris Alvarez at kalvarez@i80gold.com, phone: 775-770-4615; or Eli Witte at witteeli9@gmail.com ABSTRACT: Geologists describe rocks using lithology, alteration, color, texture, and structure, among other things. Geological observations are limited to the earth's surface and drill holes. Interpretations of geology far from these observation areas are necessarily speculative. Geophysical techniques can observe areas far from the surface and between drill holes, but do not detect these same geological characteristics. They can “see” only bulk physical properties, such as density, electrical resistivity, seismic velocity, and others. Geophysical techniques are also limited by “poor vision”, including limited detection distance, sensitivity, resolution, and masking. Density is the most easily understood physical property. It is controlled primarily by mineralogy, pore space, and pore fluid. Denser minerals, less pore space, and existence of a pore fluid all contribute to higher density. Density is detectable using gravity surveys, in which minute variations in earth's force of gravity are measured at the earth's surface, in drill holes, or from aircraft, and interpreted to estimate earth's density in 2 or 3 dimensions over a limited region. Gravity surveys are typically used to estimate sedimentary basin thickness, or detect the presence of large masses of differing density. Local gravity surveys can detect the presence of volcanogenic massive sulfide (VMS) deposits due to the higher density of sulfide minerals relative to host rocks. Electrical resistivity is the resistance of earth materials to the flow of electricity, principally alternating current within the audio-frequency range. Resistivity is controlled by mineralogy, mineral spatial relationships, porosity, and pore fluid types. Metallic-luster minerals, clay minerals, increased pore space, and conductive (salty) pore fluids decrease resistivity. Resistivity is detectable using several different geophysical techniques that involve injecting electrical current or magnetic fields into the earth. Resistivity surveys can detect VMS deposits, and can also be used to map a wide range of resistivity in three dimensions over entire project areas. Chargeability is the ability of the earth to briefly store an electrical charge. This physical property is caused by disseminated metallic-luster minerals, The magnitude of the effect is more-or-less proportional to their surface area, thus finer grain size tends to maximize the effect. Chargeability is detectable using “Induced Polarization” (IP) surveys that inject electrical current into the earth. IP surveys are most commonly used in the exploration for porphyry copper deposits, but can also used in other settings where sulfides are important. Magnetic Susceptibility is a property whereby a non-magnetic material can locally modify a vector magnetic field (normally Earth's field) that it is immersed in. This has the effect of causing local variations in Earth's field. Magnetite is the primary mineral that shows this effect. Pyrrhotite also possesses a weaker version of this physical property. Magnetic Remanence is the physical property whereby minerals are naturally magnetic and possess a local magnetic field, with north and south poles, the same as a household bar magnet. This local magnetic field combines with (adds to) Earth's dipole vector field creating local variations. These local effects can add to or subtract from the anomalies created by magnetic susceptibility. Both magnetite and pyrrhotite can possess magnetic remanence, but it can be strong, weak, or undetectable. The combined effect of both magnetic susceptibility and remanence are measured using hand-held or airborne magnetometers, Magnetic surveys are extremely useful in the search for magnetic iron ore, and also for general geological mapping in rocks that have only low concentrations of magnetite. Seismic Velocity is the speed of sound within the earth. While the speed can be measured directly, discontinuities and boundaries between layers of different seismic velocity are easier and more commonly detectable. This effect is detectable by sequentially injecting sound energy into the earth in an array of locations, and detecting the response at the earth's surface at many points in their vicinity. Seismic surveys are highly developed in the petroleum industry, but are less common in mineral exploration, due to high cost and other factors. The earth's surface emits natural gamma rays due to the presence of uranium, thorium and potassium. Each element (daughter products for U and Th) emit gamma rays of different energies. These can be detected and differentiated by gamma-ray spectrometers, some of which are small hand-held instruments, or larger more sensitive systems for airborne surveys. The most common use is as down-hole instruments in uranium exploration and development. Natural gamma rays penetrate only a very short distance (several feet) in soil, less in rock, severely limiting their 3-D utility.  
Reno, NV
Event StartsEvent Ends
05/11/202205/11/2022
All Day Event
6:00pm8:30pm