A Guide to Using the Core Orientation Program

Transcription

1 A Guide to Using the Core Orientation Program Robert Scott: Centre for Ore Deposit Research, University of Tasmania, Hobart 7001, Australia The core orientation program can be used as a calculator, with data entered sequentially via a series of input boxes (which explain the measurement conventions for the various input parameters) or by direct on screen entry. Displayed results can be stored in tabulated form. Alternately large data sets can be read from file, with results automatically stored in tabulated form, for subsequent analysis. The simple user-interface and on-screen documentation should enable effective use of the program without prior instruction or additional explanatory/reference material. However, a brief guide to using the program is presented here. The core orientation program is contained in the Excel file StructCalc.xls and Excel macros must be enabled to use the program. The file contains a number of other stand-alone structural programs, but the core program interface starts at cell [I60] on the worksheet: structural calculator. The program uses four worksheets titled: structural calculator, structural log, survey data, and from file. The sheet structural calculator contains the user-interface for the program (Fig. 1). Structural data input into the program and the corresponding calculated orientations of structural elements may be recorded in tabulated form on the sheet structural log, while down-hole survey data used by the program is stored on the sheet survey data. The program also reads tabulated input data from the sheet from file, for automatic calculation of the orientations of structural elements from large data sets. The basic structure of the program when used in sequential data entry mode (initiated by clicking the enter data button, is depicted in Figure 2. The data entry sequence is as follows. Firstly the orientation of the drill hole at the point of interest must be specified and this can be done in one of two ways. If the exact orientation of the drill hole at the point of interest is known it can be directly entered into the program (user specified), otherwise down-hole survey data (plunge and trend of the drill hole at specified down-hole depths) is entered (this data is stored on the sheet survey data ) and the hole orientation is determined by linear interpolation between the closest surveys above and below the point of interest. To distinguish between holes drilled either up- or down-plunge, negative plunges are used to specify holes drilled down-dip. However, note that dips and plunges of structural elements are quoted as positive downwards in keeping with the usual practice in structural geology.

2 Once the orientation of the drill hole has been specified, a method for reorienting the core is chosen. This can be done using the assumed orientation of either a planar or linear fabric recognised in core, or with reference to a core orientation mark, if the core is fully-oriented. Note that the layout of the user interface (e.g. Fig. 1) changes slightly depending on the choice of orientation method. If reorientation based on the assumed attitude of a planar or linear fabric in the core is chosen, the program asks for the reference orientation of that fabric. Next the angles measured in core specifying the orientation of the first or reference fabric (following the conventions described in the data entry boxes) are entered. For fully-oriented core these are foliation angle, b, and bottom-of-core reference angle, q (± lineation angle, d). If a reference plane is used only foliation angle (± lineation angle, d) need be specified. However if a reference lineation is used, both the foliation angle of the plane containing the lineation and lineation angle must be specified. Where a lineation is not developed on a planar surface, the angle the lineation makes with the core axis is entered as the foliation angle and the lineation angle is set to 0 (zero degrees). The user then has the option of entering data for a second fabric in the core (Fig. 2). Regardless of the method of core orientation used, the orientation of the second fabric is specified using the separation angle, W, between planar fabrics, the foliation angle, ± lineation angle for the other fabric. The program then calculates and displays the orientation of the fabric(s) in core. Where the core is reoriented using the assumed attitude of a reference plane, the theoretical foliation angle (based on the specified attitudes of the plane and drill hole), the minimum possible angular discordance, e min, between the plane in core and its reference orientation, and the theoretical value of q R are also displayed. If core is reoriented using the assumed attitude of a lineation, the ideal lineation angle on a plane with the specified foliation angle is determined, unless it is not possible for the reference lineation to lie on that plane. In the latter case, the theoretical angle between the lineation and the core axis is displayed. Where the attitude of a reference fabric is used to reorient core, a message box indicates whether a close (e min 10 ), adequate (e min 25 ) or poor (e min > 25 ) match to the reference orientation is possible (Fig. 11). The apparent dips of planar fabrics in any vertical section (default trend is that of the drill hole) can be calculated by clicking the button apparent dips (Fig. 2). If core is oriented using a reference fabric, the core orientation program is set up to report two solutions (at 180 to one another) if either (1) a known plane in core or its reference orientation is at 5 to the core axis, or (2) a known lineation in core or its reference orientation is at 85 to the core axis.

3 Clicking the button "Add to structural log" saves both the input data and results (Fig. 2). This gives the user the option of saving the data to an existing structural log (currently displayed on the sheet structural log ), or beginning a new log. If the currently displayed data is saved, the user is asked to name each of the fabrics present (e.g. S 0, S 1, L 2, vein, etc). Where successive calculations involve the same fabrics (for example S 1 is used as a reference fabric to determine the variation in orientation of L 1 and S 0 at multiple locations down-hole), default fabric names can be set from the Record orientation data window (Fig. 2). The current structural log can be saved as Excelworksheet from the Record orientation data window. If one wishes to use the program using the currently displayed orientation method (i.e. fullyoriented core, reference plane or reference line), input data can be entered directly into the corresponding cells (i.e. those coloured dark blue), and calculations performed by clicking the calculate now button. This is most useful where one is interested in seeing how changes in one or two of the variables affect the result. When calculations are to be performed for a large amount of input data, data is best entered (in appropriate tabulated form, Fig 3) on the worksheet from file. Orientation determinations for data on this sheet are performed automatically by clicking the data from file button on the user interface (Fig. 1). Results are automatically tabulated on the worksheet structural log. Data in tabulated form on the worksheet from file is essentially the same as that entered sequentially as described above, but there are a few important things to note. Firstly, each set of input data must occur in consecutive rows and be numbered sequentially in the first column (starting at cell [A3]). If the program encounters a blank in column A, it assumes that it has reached the end of the data set, and no data in lower rows will be used. Secondly, if drill hole orientations are to be determined from survey data entered on the worksheet survey data, only data for that hole can be entered (as in the example illustrated in Figure 3). Alternately if the user specifies the plunge and trend of the drill hole at each pint of interest, there is no limit to the number of drill holes for which data can be entered as a single block. Thirdly, the orientation method to be used for each data set, i.e. single row of data must be specified in column E (1 = Reference Plane, 2 = Reference Lineation, 3 = Oriented Core). Fourthly, names for the various fabrics can be entered in the appropriate columns (optional). These will appear on the tabulated structural log, once the program has run. Cells for which no data exists or is needed are left blank.

4 User interface of program Stores large input data sets Stores down-hole survey data used to calculate plunge and trend of the drill hole Stores structural data from the sheet "Structural calculator", entered using the "Add data to structural log" button User Guide, Figure 1. User interface of core orientation program

5 Enter orientation of drill hole: drill hole plunge, drill hole trend Enter reference orientation of known fabric: dip, dip direction (plane); plunge, trend (lineation) Enter measurements for known fabric in core: foliation angle, theta (oriented core only) ± lineation angle Enter measurements for second or "uknown fabric" in core: omega, foliation angle, ± lineation angle User Guide, Figure 2. Program layout

6 Data counter Orientation method to be used: 1= Reference Plane, 2 = Reference Lineation, 3 = Oriented Core EXAMPLE ONLY Select this worksheet to input large data sets User Guide, Figure 3. Worksheet "from file" for automatic calculations from large data sets