RESULTS FROM THE INITIAL FIELD TRIALS OF A BOREHOLE GRAVITY METER FOR MINING

AND GEOTECHNICAL APPLICATIONS

Seigel, Nind, Milanovic and MacQueen

g

Mr m

Little “g” ???

Newton’s Gedanken Experiment

Weight = Fg = m GMr2 = m g

BACKGROUND

Newton’s Law of Gravity

F = Gm1m2/r2

On the earth’s surface, for a unit mass and the earth itself, acceleration of gravity is

g = GM/R2

G = 6.67 x 10-8 cm3/gm sec2

M = 5.97 x 1027 gmR = 6.38 x 108 cm (at the equator)

Hence, at the equator, g = 978 cm/sec2

Gravity Measurement Units

• Unit: 1 Gal = 1 cm/s2

• g ~ 1000 Gal• The µGal

– 10-9 g– 3 mm height variation– Attraction of a person at close range – g on the surface of an apple sized planet

BH Gravity for Mining and Geotechnical Applications

Bulk Density Determinations• Deposit evaluation• Improved grade control• Rock properties• Relative local rock strength• Monitoring integrity of dams and tailings pondsRemote Detection• Massive Sulphide Deposits• Other Types of Metallic Deposits• Non-Metallic Deposits• Verification of Surface and Airborne Gravity Anomalies• Association of mass with conductors• Detection of Cavities and Voids

“Gravilog” BHGM SystemR&D Project, Oct ‘05 – Dec ‘08

TARGET SPECIFICATIONSensitivity < 5 uGal with 1 minute reading time Operating range 7000 mGal Sonde diameter < 48 mmSonde length Approx 2.5 m, (2.5 -4m depending upon

tool configuration )Operating depth Max. 2000 m (water filled hole)Hole diameter NQ drill rods (57.2 mm) Deviation off vertical < 60 degreesOperating temperature 0C to +70C (downhole section)

Positioning in BH +/- 5 cm (vertical), relative, between stations

GRAVILOG Sensor Housing

GRAVILOG Sensor

GRAVILOG CHAMBER

NORMAN TOWNSHIP TEST SITE

VALE INCO, SUDBURY

Vale Inco Gravilog BHGM Test

Norman Township Test Site

Vale Inco Gravilog BHGM Test

Norman Township Test Site – Mobilizing Gravilog BHGM System

Contact

LowerZone

1000m

Vale Inco Gravilog BHGM Test

Norman Township Test Site - Gravilog BHGM Setup at Drill Collar (picture of Patrick Ehoundou, Scintrex)

1000m

Vale Inco Gravilog BHGM Test

Norman Township Test Site – Gravilog BHGM Data Acquisition(picture of George Petroiu, Scintrex)

Contact

1000m

Sudbury BHGM Test

Norman Township Test Site - Looking East

Contact

Upper Zone

LowerZone

Test Hole

1000m

The hole “intersects sulphides from 1400m to 1480m, but the upper half of this interval is very weak, disseminated mineralization averaging 10-20% Sulphide (SG= 2.8-3). The lower half of the intersection is much better consisting mostly of massive to semi-massive sulphides grading above 50% Sulphide (SG=3.5-4).”(courtesy of Vale Inco)

Sudbury BHGM Test

Norman Township Test Site - Plan View

Contact

Upper Zone

LowerZone

Test Hole

1000m

INTERSECTIONRESPONSE

GRAVILOG BHGM SYSTEMNORMAN TOWNSHIP TEST SITE, VALE INCO, SUDBURY, ONTARIO

December 12 – 14, 2008

Station(metresdownborehole)

Norman Test : Residual Gravity

1400 m

BULK DENSITY

Bulk density of formation between gravity readings

ρ = [-1/(4πG)] (Δg / Δz)

= -11.93 (Δg / Δz) .. g/ccΔg in milligalsΔz in metres

BULK DENSITY

Note: Density determination after normal terrestrial gradient (0.30861 mG /m) removal.

Bulk Densities obtained from data collected on the both runs (top to bottom and bottom to top) using a proprietary algorithm for calculating bulk densities, developed by Dr. Jeff MacQueen at Micro-g LaCoste.

Mean Bulk Density 2.767 g/cm3

GRAVILOG BHGM SYSTEMNORMAN TOWNSHIP TEST SITE, VALE INCO, SUDBURY, ONTARIO

December 12 – 14, 2008

SHEA CREEK TEST SITE

AREVA RESOURCES CANADA, SASKATECHWAN

AREVA Resources Gravilog Test

Shea Creek Test Site, Athabasca Basin, Saskatchewan

AREVA Resources Gravilog

Test

Shea Creek Test Site

Mineralization

Shea Creek Test SiteGamma Log, 680 – 755 m

March 26, 2009

NEAR MISSRESPONSE

Shea Creek Test SiteGravilog Bulk Density

March 26, 2009

Shea Creek Test Site: Residual Gravity

-0.500

-0.400

-0.300

-0.200

-0.100

0.000

0.100

0.200

0.300

0.400

0.500

0 100 200 300 400 500 600 700 800 900

Depth (metres down hole)

Resi

dual

Gra

vity

(mill

iGal

)

Shea Creek Test SiteResidual Gravity, 75 – 825 m

March 26, 2009

UnconformityAthabasca Sandstone (2.5 g/cm3)

Archean Basement

(2.67 g/cm3)

(data processed by Seigel, 2009)

GRAVILOG - Status• Prototype production tool successfully tested in two NQ exploration boreholes

- Small gravity sensor performed well, sensitivity < 5 microGal with 1 minute reading

- Leveling system performed well unless borehole is vertical- Rotation of probe appears to correlate with offsets in measurements

- Avoid rotating probe during operation (off vertical borehole, wings, cable handling)

- Design modified to reduce thermal asymmetries- Clamp worked well- Pressure sensor provided accurate relative depths- Depth down hole provided by counter – worked well- CCL does not work in NQ casing- Gamma works well- Telemetry (DSL modem) worked well- Uphole electronics and winch worked well- Production rate for 10 metre station interval: 7 minutes between stations

GRAVILOG Development – Commercialization

• Second Gravilog system has been built at Scintrex- The gravity module is less than 2 metres long, but auxiliary systems

increase the total sonde length to 4 metres. A flexible joint is being tested, which would make the sonde easier to handle

• Field trials for BHPB and Schlumberger have been delayed on their requests

• Data acquisition on the first commercial Gravilog survey was completed in early October, 2009. The data is now being analyzed.

• Borehole gravity is commercially available for mining applications

CREDITS

Scintrex thanks Vale Inco and AREVA for the excellent support provided to the Scintrex Gravilog crew during the Norman and Shea Creek field tests

Thank you to the sponsorship group • CAMIRO – Tom Lane• Vale Inco – Kevin Fenlon, Glenn McDowell• BHP Billiton – Peter Diorio• AREVA – Kevin Crain, Grant Nimeck• Schlumberger – Harold Pfutzner• IRAP – Ramesh GuptaAnd to the educational institutions• Sir Sanford Fleming College• Ecole Polytechnique de Montréal

THANK YOU