This SURFER problem shows a reconnaissance contour-map procedure for outlining two structurally and stratigraphically controlled lead-zinc deposits. The ore is localized in a limestone-dolostone formation that varies in thickness from about 30 to 130 feet and ranges from 0 to 65 percent dolostone. The dolomitic facies contains the greatest concentrations of sphalerite and galena ore.

The data set contains 20 core logs, which include the identifcation number, the top elevation (feet above msl), bottom elevation, and the percent dolostone of the formation. Also included is a map showing a site-coordinate grid and the mapped trace of a near-vertical fault that transects the formation.

Areas where the dolostone content of the formation exceed 50 percent contain profitable ore. The objective will be to use Surfer to delineate the areas of profitable ore within the mapped area.

Procedure:

A. Use either Notepad, Excel, or a Surfer worksheet to create a Surfer BLN file for the fault. See the Surfer help files for the correct format. Spatial coordinates (northeast to southwest) of the fault follow: (6250,4785), (4250,3500), (2500,2800), and (1500,2700). Save this file and include it as a fault line when creating grids.

B. Create two contour maps: one of the top of the formation, the other of the bottom. Use the default x-y margins for the maps and be sure to include the fault when generating the grid.

C. Use Surfer's  grid math command to derive the isopach (thickness) contour map for the formation.

D. For the final map, show the isopach contours (10 foot contour interval) and shade the map in areas where the dolostone content exceeds 50%.

Extra Credit: Estimate the volume of ore in the mapped area. (Hint: you probably will need to generate an indicator grid. Assign grid points in areas where dolostone exceeds 50% a "1" and other areas (<50%) a "0". Use the grid math command to multiply the indicator grid times the thickness, then use the the volume command. See the help files or the manual for more details).