stimulating exploration in the east kootenays (seek ... · the individual aris gravity datasets...

Stimulating Exploration in the East Kootenays

(SEEK Project):

East Kootenay Gravity Database

T. Sanders1

1 Ted Sanders Consulting, Fernie B.C.; [email protected]

November, 2012

Geoscience BC Report 2012-12

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1 INTRODUCTION ................................................................................................................................. 2

2 REGION COVERED BY GRAVITY DATABASE ........................................................................... 2

3 DESCRIPTION OF THE EKGDB ...................................................................................................... 2 3.1 Database Field Names and Descriptions ................................................................................... 3/4

4 GRAVITY DATA SOURCES .............................................................................................................. 5 4.1 Data Source Citations .................................................................................................................... 5 4.2 Mineral Titles Online – ARIS ........................................................................................................ 5 4.3 GSC Gravity Database ................................................................................................................... 5 4.4 Contribution by BK 98 Joint Venture Claim Group ................................................................. 5

5 EVALUATION OF GRAVITY DATA SOURCES ........................................................................... 6 5.1 Assessment Reports on ARIS Website ......................................................................................... 6 5.2 GSC Gravity Data .......................................................................................................................... 6 5.3 Digitized Map Data on ARIS website ........................................................................................... 7 5.4 BK 98 Joint Venture Claim Group Gravity Data ....................................................................... 7 Table 2 ....................................................................................................................................................... 8

APPENDIX: ARIS Survey Specifications and Adjustments

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1 INTRODUCTION

The East Kootenay ground station Gravity Database is a component of the Stimulating Exploration in the East Kootenays (SEEK) program. This project is sponsored by Geoscience BC in partnership with the East Kootenay Chamber of Mines.

The majority of gravity data in the East Kootenay Gravity Database (EKGDB) was obtained from data listings in assessment reports on the Mineral Titles Online ARIS (Assessment Report Indexing System) website (www.empr.gov.bc.ca/mining/geoscience/aris/pages/default.aspx). Other sources include: contributed data from gravity surveys not presently available on the ARIS website, a subset of the Geological Survey of Canada (GSC) database, and a digitized Bouguer Anomaly posting map (obtained from an ARIS file which did not contain raw data).

All of the original gravity data listings in the ARIS pdf files include Bouguer Anomaly values for each station. However, Bouguer Anomaly values from different contractors used different data reduction formulae and parameters. Some processing errors were also detected in the raw data listings. As a result, leveling adjustments have been made to some of the ARIS GPS survey data, Observed Gravity values, and Bouguer Anomaly data prior to reprocessing and the creation of a uniform Gravity Database. In addition, 30 km Outer Terrain Corrections were calculated for each station as part of data reduction to Bouguer Anomaly values in the database.

This project enables users to download digital (.csv) files of the original ARIS gravity data listings and raw Inner Terrain Correction data. In addition, the complete database (27 fields) can be downloaded and includes raw and reduced Bouguer Anomaly values for all stations using three rock densities.

2 REGION COVERED BY GRAVITY DATABASE

The geographical boundaries for the EKGDB are Latitudes 49o00’ to 50o00’ North, and Longitudes 115o30’ to 117o’00 West, spanning the east half of NTS 82F and the western quarter of 82G (Figure 1). Kootenay Lake is near the western margin of the area and the Purcell Rocky Mountain Trench is near the eastern margin. All station locations are referenced with latitude and longitude coordinates, as well as Universal Transverse Mercator (NAD83) coordinates.

The individual ARIS gravity datasets included in the EKGDB are concentrated in several sub-regions within the area defined above and include the St. Mary Lake/Matthew Creek area, the Wildhorse River and Moyie River drainages, Cranbrook, Crawford Bay, and regions east and west of Yahk, B.C.

3 DESCRIPTION OF THE EKGDB

The complete EKGDB contains records for over 4860 individual ground gravity stations. The three database source types, described above, share many common fields but some fields contain data for only one of the source types. Each data record has been given a unique record number (“vector”). The three database source types are:

1) ARIS (and contributed) data (3646 stations, vectors 1-3646), 2) GSC data (485 stations, vectors 3647-4131), and 3) Tied Bouguer Anomaly values from a digitized map (735 stations, vectors 4132-4866)

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Figure 1. Location map for East Kootenay Gravity Database.

The database listing contains 27 fields, and shows all relevant data from the raw and processed gravity data. The first 23 fields relate to the complete leveled, adjusted and reprocessed gravity data. Fields 24 and 25 show the original ARIS station elevations and any elevation adjustments made, respectively. Field 26 contains an interpolated DEM Elevation for each listed GSC station coordinate (for analytical purposes) and has no bearing on the processed gravity data. Field 27 contains the original Bouguer Anomaly (density 2.80) values for the station locations from the digitized map in ARIS 13748. Fields containing no data (blanks) have been filled with the value -9999.

The database includes a supplemental 30 km Outer Terrain Correction (OTC) calculated at rock density = 2.67 gm/cc for each station. Each OTC utilized an inner radius that is complementary to the outer radius of the Inner Terrain Correction (ITC) used. OTC’s were calculated using DEM data extracted from the GeoBase Canadian Digital Elevation Data (CDED) website and proprietary Terrain Correction software, with permission from Brian Jones of Excel Geophysics, High River, Alberta.

3.1 DATABASE FIELD NAMES AND DESCRIPTIONS

Table 1 contains the field names used in the EKGDB and a brief description for each field. For more information on each data type, refer to section 5.

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Table 1. EKGDB Field Names and Descriptions.

Field Name Field Description

Vector Unique record number within the database Source ARIS Report Number (if available), “GSC” for GSC data, -9999 for contributed data

Line_Project Line Number (if used), Project Number (for GSC data)

Station Station Number

UTMX_Z11 UTM Easting (NAD83, zone 11)

UTMY_Z11 UTM Northing (NAD83, zone 11)

LAT Latitude (NAD83)

LONG Longitude (NAD83)

ELEV Adjusted Elevation (= “ELEV_orig” + “Adjust” value)

OBSGRAV Observed Gravity: tied to Canadian Gravity Standardization Network (CGSN)

LAT_COR Latitude Correction: (uses WGS84 formula - shown below Field Name list)

FA_COR Free-Air Correction (=ELEV * 0.03086)

BG_COR Bouguer Correction (=ELEV * -0.04192 * 2.67 (density))

50mITC 2-50 metre Inner Terrain Correction (density 2.67), ARIS data




30kOTC 30 km Outer Terrain Correction (density 2.67), calculated

22kTC267 Original GSC 22 km Terrain Correction (density 2.67)

30kTC267 22-30 km Terrain Correction for GSC data (density 2.67)

Bougan267 = OBSGRAV – LAT_COR+ FA_COR + BG_COR + ITC* + 30kOTC**

Bougan275 = OBSGRAV – LAT_COR + FA_COR + 2.75/2.67 * (BG_COR + ITC* + 30kOTC**)

Bougan280 = OBSGRAV – LAT_COR + FA_COR + 2.80/2.67 * (BG_COR + ITC* + 30kOTC**) ELEV_orig Original elevation from ARIS data listing

Adjust Elevation Adjustment (metres)

DEM_elev Interpolated DEM elevation at GSC station location

Orig_Boug280 ARIS Report 13748 original Bouguer Anomaly value for station * ITC:uses only one of the four ARIS ITC fields or 22kTC267 for GSC data, see Section 5.1

** GSC data uses 30kTC267 instead of 30kOTC

WGS84 Latitude Correction formula used:

978032.67714*(1+0.00193185138639*Sin(LAT)2 )/(1-0.00669437999013*Sin(LAT)2 )0.5

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4 GRAVITY DATA SOURCES

4.1 DATA SOURCE CITATIONS

BC Ministry of Energy and Mines (2012): ARIS assessment report indexing system; BC Ministry of Energy, Mines and Petroleum Resources, URL <http://aris.empr.gov.bc.ca> [May 2010].

Natural Resources Canada (2012): Canadian Geodetic Information System; Geoscience Data Repository, Geodetic Survey Division, Earth Sciences Sector, Natural Resources Canada, URL <http://gdrdap.agg.nrcan.gc.ca/geodap/home/Default.aspx?lang=e> [Dec 2011]

Excel Geophysics Inc., Fort Steele Gravity Survey, Ft. Steele, British Columbia, Canada;

BK 98 Exploration Gravity Joint Venture Claims Fund (December, 2010; April, 2011)

National Topographic Data Base (NTDB): Canadian Digital Elevation Data (CDED), B.C. Data Sources > T.R.I.M. 1:20,000, URL ,<http://www.geobase.ca/geobase/en/data/cded/index.html>[Dec 2011]

4.2 MINERAL TITLES ONLINE – ARIS

Most of the ARIS pdf files acquired were scanned from hard-copy reports and therefore the gravity data listings were not in digital format. Listings of raw and processed gravity data for over 2800 individual gravity stations from 17 individual ARIS files were scanned and converted to digital format as part of this project. To date (July, 2012), the acquired ARIS files containing gravity listings in the East Kootenays are:

• 24687 • 25271 • 25395 • 25527 • 25590 • 29738

• 24786 • 25326 • 25467 • 25555 • 25715 • 30170

• 25217 • 25348 • 25526 • 25567 • 28454

In addition to the above, over 700 station locations with annotated Bouguer Anomaly values were digitized from a Bouguer Anomaly Map in ARIS 13748 (1984).

4.3 GSC GRAVITY DATABASE

Gravity data for 485 stations (acquired between 1954 and 1979) was extracted from the GSC Gravity Database, available on the NRCAN website. See section 5.2 for details.

4.4 CONTRIBUTION BY BK 98 JOINT VENTURE CLAIM GROUP

The BK 98 Gravity Survey Joint Venture Claim Group has generously agreed to contribute data to this project. Approximately 800 gravity stations acquired in October 2010 and April 2011 on behalf of this group are included in the database.

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5 EVALUATION OF GRAVITY DATA SOURCES

5.1 ASSESSMENT REPORTS ON ARIS WEBSITE

Listings containing raw and processed gravity data were located in seventeen Mineral Titles Online assessment reports (see section 4.2). Mining companies or prospectors contracted these ground gravity surveys. All data listings contained Bouguer Anomaly values for each gravity station, however, not all listings were complete. In addition, not all gravity surveys were processed to Bouguer Anomaly using the same reduction formulae and parameters and some minor errors were detected. Therefore, it is not possible to correctly merge the original processed Bouguer Anomaly values from each survey together for mapping.

All gravity station coordinates in the seventeen ARIS files were acquired by GPS surveying methods. However, some GPS surveys were not referenced to Canadian Geodetic Control Monuments and used an autonomous GPS fix for base station coordinates. As a result, elevation adjustments (bulk shifts) have been made to a few groups of stations based on a combination of:

1) comparisons of station coordinates to the local Digital Elevation Model, and 2) comparisons of station Bouguer Anomaly values to nearby stations from surveys tied to Geodetic

Control monuments.

The database field labeled “ELEV_orig” displays the original station elevations. The field labeled “Adjust” shows any elevation adjustments (in metres) added to the original elevations to attain the “ELEV” field used for data reduction in the database.

Latitude/Longitude and UTM coordinates for the survey in ARIS 25715 were also tied to a GPS base station coordinate established by autonomous fix. All station UTM x, y, z coordinates were found to have a significant GPS error and were adjusted. Observed Gravity values for one survey (ARIS 25217) were found to be incorrectly tied to the National Gravity Absolute Network and were corrected. Specifications for the original gravity surveys and any adjustments to original raw data for each ARIS survey have been noted in the appendix.

Four different outer radii for Inner Terrain Corrections were used in the ARIS data listings however each database record only uses one of the four ITC fields listed in the database. Most of the original ARIS gravity data listings did not contain an Outer Terrain Correction (OTC) which is necessary for complete data reduction in mountainous terrain. The database includes a calculated 30 kilometre OTC for each station at rock density = 2.67 gm/cc. Each OTC utilized an inner radius that is complementary to the outer radius of the ITC used. OTC’s were calculated using DEM data extracted from the CDED website and proprietary Terrain Correction software, with permission from Brian Jones, from Excel Geophysics, High River, Alberta.

Additional details of original ARIS survey specifications and adjustments are provided in the appendix.

5.2 GSC GRAVITY DATA

The GSC gravity data is available for free from the Natural Resources Canada (NRCan) website. The vintages of the GSC data in the East Kootenay region range from 1954 to 1979. Relevant information regarding the GSC raw and database fields are provided in table 2. Data quality is good to very good in areas with roads and culture. In mountainous areas, data quality is less accurate due to positioning and the

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original 22 km Terrain Corrections (containing both Inner and Outer Corrections). Overall, the GSC data quality is good.

The GSC data are made available to users under the terms of the Geogratis Licence Agreement and are copyright © Department of Natural Resources Canada. All rights reserved. The complete agreement can be found at: www.geogratis.ca/geogratis/en/licence.jsp.

5.3 DIGITIZED MAP DATA ON ARIS WEBSITE

Station locations (735) were digitized from a Bouguer Anomaly map obtained from ARIS 13748, and the annotated Bouguer Anomaly values from the map were key-entered for each station location. The digitized UTM coordinates (NAD27) were transformed to NAD83. The gravity data was processed at density 2.80 gm/cc and included a terrain correction (no radius given) but no raw data was included in the file. The database field “Orig_Boug280” provides the original Bouguer Anomaly values from the map. These values were compared to reprocessed local GSC Bouguer data and adjusted by a constant to tie to the database for the three database densities (2.67, 2.75, and 2.80). Data quality is considered fair to good.

5.4 BK 98 JOINT VENTURE CLAIM GROUP GRAVITY DATA

This gravity data was acquired in 2010 and 2011 and will be released on the ARIS site in early 2013. The GPS survey was tied to Geodetic Control Monuments and the data is of excellent quality. Presently, these data are included in records (vectors) 2830 to 3646 of the database.

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Table 2. EKGDB fields and relevant information for GSC data points

Field Name Relevant information for GSC Data

Line_Project Number First four digits: year of survey Last three digits: specific survey ID number

Geographical Coordinates These were often estimated from cultural markers (i.e. roads, trails, power lines, bridges, railways, etc.) on topographic maps. GSC Station UTM coordinates were converted from Latitude and Longitude (NAD83) provided with the GSC data.

ELEV (Elevation)

Often used barometric altimeter data. GPS was not available.

OBSGRAV (Observed Gravity)

Tied to CGSN, rounded to 0.1 mGals

22kTC267 (22km Terrain Correction)

This is the original GSC Terrain Correction. It is the sum of an (2 to 170 m) Inner Terrain Correction (calculated using field estimates at the time of gravity reading) and an (170 m to 22 km) Outer Terrain Correction calculated by hand using Hammer charts and 1:50,000 scale topography maps. It is not possible to separate the two components. Inaccurate Terrain Corrections may exist in mountainous terrain, but adjustments have not been made to this field.

30kTC267 (30km Terrain Correction)

This data field is not included with the original GSC data. It is a supplementary 22-30 km Terrain Correction calculated using the GSC 1 km Digital Terrain File and proprietary Terrain Correction software, by permission from Excel Geophysics, High River, Alberta, in order to provide a matching 30 km Terrain Correction for each station in the Digital Database.

DEM_elev This data field is not included with the original GSC data. It is an interpolated elevation derived from the DEM at the GSC gravity station coordinate. It is for comparative purposes only and has not been used in any database field calculations.

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Appendix: ARIS Survey Specifications and Adjustments

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ARIS Number: 30170

Project Name: Lone Group Gravity Survey

Project Location: Mause Creek

Month/Year of Survey: August, 2007

Gravity Survey Specs

Gravity Survey Contractor: MEG Systems, Calgary, AB

Gravity Base Station Location: Cranbrook Post Office #9025-1980 (980699.79)

Intermediate Gravity Base Station Location: TBM1_Heritage Motel, Cranbrook - tied to #9025-1980

Intermed. Gravity Base Station Value (mGals): 980697.60 (TBM1)

Gravity Meter(s) Used: Lacoste&Romberg model G-239

Positional Survey Specs

Survey Type / Equipment: GPS / Leica System 500 RT

Positional Control: Established by 15 min. Autonomous Fix

Survey Method: Real-Time and Static Differential

Geodetic Ellipsoid/Datum: WGS84/NAD83

Gravity Data (Listing) Parameters

Number of Stations Acquired: 58

Number of Stations in Listing: 315 (includes 225 stations from ARIS 28454 + 31 from ARIS 29738 + 1 Base(999))

Theoretical Gravity Formula (Latitude Correction): g = 978031.846*(1 + 0.005278895*(sin LAT)^2 + 0.000023462*(sin LAT)^4)

Free-Air Correction: Elevation (ASL) * 0.3086 mGal

Bouguer Correction: Elevation (ASL) * 0.04192 * density (2.45)

Inner Terrain Correction: Hammer zones B, C & D (170m) @ density 2.45

Outer Terrain Correction: 30km (density 2.45)

Density of Bouguer Anomaly values: 2.45

Additional Information

Unique stations for this report are Lines 4_07, 5_07, 6_07, 7_07, 8_07, 9_07

ObsGrav and LatCorr values in listing are rounded to 0.1 mGals

Lat / Long values rounded to 4 decimals in notes, database Lat / Long recalculated from UTM coords.

GPS not tied to Geodetic Control Monuments - Elevation Adjustments made

Latitude Correction formula in report (pdf page 17/53) is incorrect.

No raw ITC data included in report

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ARIS Number: 29738 Project Name: Boulder Gold Gravity Survey

Project Location: Wildhorse Creek Area near Ft. Steele






Intermed. Gravity Base Station Value (mGals): 980697.60

Gravity Meter(s) Used: Lacoste&Romberg model G-239



Positional Control: Base 999 - Established by 15 min. autonomous fix

Survey Method: Real-Time and Static Differential



Number of Stations Acquired: 31 + 1 at GPS base

Number of Stations in Listing: 31

Theoretical Gravity Formula (Latitude Correction): IGF GRS1967 (var.)


Bouguer Correction: Elevation (ASL) * 2 * pi * 0.006672 * density 2.00

Inner Terrain Correction: Hammer zones B & C (53.3m) @ density 2.00

Outer Terrain Correction: n/a

Density of Bouguer Anomaly values: 2.55, 2.60, 2.65


These data are also included in ARIS 30170 listing (with 30km Outer Terrain Corrections)

GPS not tied to Geodetic Control Monuments - Elevation Adjustment not required

No ITC data included in report

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ARIS Number: 28454

Project Name: Mause Creek/Wildhorse

Project Location: Mause Creek/Wildhorse

Month/Year of Survey: July, 2004 / June, 2005 / December, 2005






Gravity Meter(s) Used: Lacoste & Romberg model G-



Positional Control: Established by Autonomous Fix

Survey Method: Real-Time Kinematic / Static Differential


Gravity Data (Listing) Parameters Number of Stations Acquired: 96

Number of Stations in Listing: 293 (includes 53 from ARIS 25555)



Bouguer Correction: Elevation (ASL) * 0.04192 * density (2.45)

Inner Terrain Correction: Hammer zones B, C & D (170m) @ density 2.45

Outer Terrain Correction: 30km @ density 2.45



ObsGrav and LatCor values in listing are rounded to 0.1 mGals

GPS not tied to Geodetic Control Monuments - Elevation Adjustments made

Report contains 2 sets of gravity listings - 2nd listing contains data for Lines 9 & 10, Obsgrav was reverse engineered

Data listed as Line 1997 were obtained from ARIS 25555 - key-entry & processing errors were noted

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Caution: ITC values for L1997 were copied from ARIS 25555 (den 2.67) and processed as density 2.45

No raw ITC data included in report

ARIS Number: 27747

Project Name: Sully Properties Gravity Survey

Project Location: Brewery Creek / Wildhorse River Area

Month/Year of Survey: July, 2004






Gravity Meter(s) Used: Lacoste&Romberg model G-

Positional Survey Specs Survey Type / Equipment: n/a

Positional Control: n/a

Survey Method: Static Mode




Number of Stations in Listing: data listing included in ARIS 28454

Theoretical Gravity Formula (Latitude Correction): see ARIS 28454

Free-Air Correction: see ARIS 28454

Bouguer Correction: see ARIS 28454

Inner Terrain Correction: see ARIS 28454

Outer Terrain Correction: see ARIS 28454

Density of Bouguer Anomaly values: see ARIS 28454


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ARIS Number: 25715

Project Name: Doe-Ray

Project Location: Crawford Bay

Month/Year of Survey: October, 1997


Gravity Survey Contractor: Quadra Surveys


Intermediate Gravity Base Station Location: Base -101 (Klondike Gold Office, Wilks Road, Cranbrook (980688.13) / Base -271 (Crawford Bay)

Intermed. Gravity Base Station Value (mGals): 980688.13 (-101)

Gravity Meter(s) Used: Scintrex CG-3 (#10345)


Survey Type / Equipment: Trimble Surveyor 4400 / Paciifc Crest radio link

Positional Control: Established by autonomous fix (adjusted for final database)

Survey Method: Real-Time & Rapid Static



Number of Stations Acquired: 47 + 1 Base station




Bouguer Correction: Elevation (ASL) * 2 * pi * 0.00667 * density (2.67)

Inner Terrain Correction: Hammer zones B, C & D (2-170m) @ density 2.67




GPS Base established with Autonomous GPS fix - major problem with coordinate

(many original station locations post in water, on houses, private property or heavily forested areas)

> A utm coordinate adjustment of (x+67, y-157) moves all stations to roadsides, trails or open lots.

> After UTM fix, an Elevation Adjustment of +12 metres for all stations provides best fit to DEM

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ARIS Number: 25555

Project Name: Kootenay King

Project Location: Ft.Steele / Wildhorse River





Intermediate Gravity Base Station Location: Base -101 (Klondike Gold Office, Wilks Road, Cranbrook (980688.13)





Positional Control: Tied to Canadian Geodetic Control System




Number of Stations Acquired: 52 + 2 Base stations





Inner Terrain Correction: Hammer zones B, C & D (2-170m) @ density 2.67 , raw ITC data in degrees




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ARIS Number: 25590

Project Name: Clair West

Project Location: St. Mary River Area

Month/Year of Survey: September, 1997






















17

ARIS Number: 25567

Project Name: Panda Basin

Project Location: Moyie River Area























18

ARIS Number: 25527

Project Name: Espiritu Claims

Project Location: Cranbrook Area























19

ARIS Number: 25526

Project Name: Strata, Form, Spirit, and Fran Claims

Project Location: Moyie Lake Area

Month/Year of Survey: September, 1997






















Lat-Long coordinates rounded to 2 decimals in notes

Lat-Long in database converted from utm coordinates

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ARIS Number: 25467

Project Name: Lew & Bingo Claims

Project Location: Moyie River Area

Month/Year of Survey: June, 1997






















21

ARIS Number: 25395

Project Name: PP Claims

Project Location: Lamb Creek Area























22

ARIS Number: 25348

Project Name: Roll, Lill, and Kitch Claims

Project Location: Goat River Area

Month/Year of Survey: July-August, 1997






















23

ARIS Number: 25326

Project Name: Pyramid Peak

Project Location: St. Mary River / Pryramid Peak Area























24

ARIS Number: 25271

Project Name: Pyramid Peak

Project Location: St. Mary River / Pyramid Peak Area























25

ARIS Number: 25217

Project Name: Ham Gravity Survey

Project Location: Matthew Creek Drainage near Kimberley










Positional Control: Tied to Canadian Geodetic Marker #543249 (897050)













Lat-Long coordinates rounded to 2 decimals in notes

Lat-Longs in database converted from original UTM coordinates

Observed Gravity values tied to incorrect Base value. 3.0 mGals added to all Obsgrav values

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ARIS Number: 24786

Project Name: Chubby, David, Lewis, LMC, MCL, Moyie, etc. Claims

Project Location: South Moyie River Area southwest of Cranbrook

Month/Year of Survey: August-September, 1997






Gravity Meter(s) Used: Lacoste&Romberg G-230, G-164


Survey Type / Equipment: Leica 299 and 399 DD/Leica SKI software

Positional Control: Tied to Canadian Geodetic Markers - GBM #850049/G1355

Survey Method: Rapid Static








Inner Terrain Correction: n/a




No Inner Terrain Correction notes or values included

> 55 metre ITC estimated using DEM

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ARIS Number: 24687

Project Name: Weaver Claims Geophysical Report

Project Location: Weaver Creek (Moyie River Area)

Month/Year of Survey: October, 1995 - September, 1996


Gravity Survey Contractor: Excel Geophysics Inc.


Intermediate Gravity Base Station Location:

Intermed. Gravity Base Station Value (mGals):

Gravity Meter(s) Used: Lacoste&Romberg G-211, G-732, G-232, G-239


Survey Type / Equipment: GPS Differential / WILD/SKI software

Positional Control: Autonomous fix based on 2 days of data

Survey Method: Rapid Static







Bouguer Correction: Elevation (ASL) * 2 * pi * 0.00667 * density (2.00

Inner Terrain Correction: Hammer zones B, C & D (2-175m) @ density 2.00

Outer Terrain Correction: 175m-10km @ density 2.00

Density of Bouguer Anomaly values: 2.60, 2.70, 2.80


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