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Geology/disseminated sulfide deposits

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QUESTION: Dear sir,
         which geophysical method is used for exploration of disseminated sulfide deposits ? can gravity method(CG-5 Auto grave) helped to explored it based on gravity ?

regard:
waqar
pakistan

ANSWER: Dear Waqar, Fraternal greetings!, Please find herewith the answer to your question:

In the mining industry, gravity is still widely used as an exploration tool to both map
Sub- surface geology and help estimate ore reserves for some massive sulfide orebodies.


Crone, J.D., 1979, Exploration for massive sulfides in desert areas using the ground pulse electromagnetic method, in Geophysics and geochemistry in the search for metallic ores,

Hood, P.J., ed.:
Method:          Electrical resistivity method
Application media:      Ground, marine, drill-hole logging
Sulfide deposits, conductive vs resistive rocks, massive sulfides etc

Method:          Electrical induced polarization
Application media:      Ground, drill-hole logging
Disseminated and massive sulfides

Method:          Electrical self-potential
Application media:      Ground, drill-hole logging
Sulfide ores

CG-5 Autograv Gravity method is also useful in the following
To detect Volcanic Massive Sulphides deposits associated with nickel deposits, diamond bearing Kimberlites, Banded Iron Formations, and Impact Basins. This method can also be used to determine the size of the deposit.
Scintrex products such as the CG-5 AUTOGRAV™ Gravity Meter and ENVI Proton Magnetometer are the rocks the companies build upon. These high tech instruments provide fast and accurate measurements to aid in determining what lies beneath the surface.
The sensing element of the CG-5 AUTOGRAV is based on a fused quartz spring system. The gravitational force on the proof-mass is balanced by a spring, and an electrostatic restoring force. The inherent strength and excellent elastic properties of fused quartz, together with the limit stops around the proof-mass, permit the instrument to be operated without clamping. Additional protection is provided by a durable shock mount system. The CG-5 AUTOGRAV incorporates the gravity sensor, control keypad, electronics, and batteries into one lightweight weather resistant instrument case. No cables to trip over, no handheld devices, just an easy to use and carry, self-contained gravity meter. The CG-5 AUTOGRAV is equipped with a radio-frequency remote start transmitter (keyfob) to allow measurement to be taken without disturbing the meter by touch. By using the electronic tilt sensors, the CG-5 AUTOGRAV is constantly updating information from the internal tilt sensors. The CG-5 AUTOGRAV can automatically compensate measurements for the errors in instrument tilt. This operator selectable feature ensures that when measurements are taken on unstable ground, errors due to instrument movement are automatically eliminated. Based on operator entered geographical location and time zone data or GPS information, the CG-5 AUTOGRAV can automatically calculate and apply a real time tidal correction to each reading.


---------- FOLLOW-UP ----------

QUESTION: what indication If we got negative gravity anomaly ? and what if positive Anomaly by Cg-5 grave meter ?
and we determine the subsurface fault  by this method ?

Answer
Dear Waqar

My answer is given below for your follow up question.

The positive and negative signs for different ore bodies are given. We can determine the sub surface fault by using these methods also.

Gravity signatures from relatively shallow density contrast sources have historically been used in both mineral and hydrocarbon exploration to identify any important geologic targets for which there was a density contrast at depth. Examples include:

Ore bodies (+),
Salt domes, shallow salt where sediments are of low density (+),
Salt domes, deep salt where sediments are of higher density (-),
Sulfur (complex distribution), Basin geometry (-),
Reefs (+ or - , depending on porosity and depth),
Carbonate leading edges of thrust sheets (+),
Faults (gradient lineaments, down-thrown or footwall side indicated by lower gravity),
Anticlines and horst blocks (+),
Regional geology (complex distribution and gradient lineaments), and
Kimberlite pipes (+ or - , depending on country rock and degree of weathering).  

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Dr D S Subrahmanyam

Expertise

All questions related to Geology, Geotechnical Engineering (especially in-situ stress, in-situ Deformability and Shear investigations) required for underground tunnels and excavations, Dimensional Stone Mining. Can't answer Soil dynamics related to Geotechnical Engineering

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Geology and Geotechnical Engineering and Dimensional Stone Mining

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National Institute of Rock Mechanics (Govt of India)

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International Journal of Mining Engineering and some other Indian journals

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Doctorate in Geology

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Reviewer for 3 International Journals

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