Show 01 17 1 7 ar 4 4 oil W h t 0 y pa W A aall 44 44 x wet we T va pet Z ve V ZO W A i 0 this picture of old tune time freighting with team and wagon on the green river desert is used be cause it shows the type of terrain the ore carriers meet on the temple mountain haul some of the roads that modern trucks must negotiate are no better than the one pictured driller inquiry draws answer on probing my probe reading starts climbing at 67 feet reaches 33 per cent at 68 and is down to background at 69 feet do I 1 have enough ore to go this or a similar problem arises quite frequently in this business of probing drill holes unfortunately there is no simple answer to this mans question his data are insufficient even to estimate what thickness of ore or grade he has in the hole A logging probe which is corn com plemely surrounded by ore on all sides and to a considerable dis tance above and below the probe will give an accurate radiometric assay of that ore however it if these conditions are not met or the ore is not in radiometric equilibrium the results can be very misleading radiometric equilibrium means simply that the rays gamma rays in the case of a logging probe are in direct proportion to the ithe uranium content of the ore to be N in this condition the ore must have been in place and not modified by additon or removal of uranium oxide and the strong gamma en emitting utting elements uxa uxa and radium C and D 8 im mil ion years is required to reach this state there is only one sure way to prove if an ore is in equilia num a comparison of chemical and radiometric analysis even if an ore is not in actual equilibrium a ration or correction between radiometric and chemi I 1 cal analysis can be used if a sam pie is compared af after ter radon gas has been equalized after 20 days such a sample or standard will win be useful for many years it should be taken from the mine or as near to actual conditions of the test holes as possible A ered outcrop for instance is use less for us as a sample for holes back beyond the outcrop A sam pie from a similar mine of a simi lar type ore would be better in this case but still should be used with discretion if the probe tube is not fully surrounded by ore then other factors must be considered pic ture a tube being lowered through a hole in barren ruck rock at a sharp face there is an ore body As the tube approaches the ore face it sees the ore on the side of the hole some distance up the hole and begins to count the amount it sees I 1 is a function of the diameter of the bore hole and the thickness of the ore As the tube approaches within about 1 foot of the ore it begins to pick up gammas that came from a dis tance back of the hole side and have penetrated the country rock so another source of rays becomes effective then as the tube enters the ore the angle of ore it sees becomes larger until at a point about 3 hole diameters down the angle is to all practical purposes constant the probe now is in a position to give a proper radio metric assay and remains so until it nears 3 hole diameters of the bottom edge of the ore if the ore faces are not a sharp ime line but high grade tapers off into barren rock the picture is fur ther complicated by this change of grade furthermore because the tube is a certain length usually 3 a or r 4 inches the tube length or a portion of it is add ed to the a apparent thickness of the ore in the case of a thin seam that is thinner than the active length of tube the picture is still more complicated since the geometrical relationships of seeing the ore the effect of gammas pene trat ing the rock on each side of the ore and the effect of the tube length are far more complex As an example a in thick seam of high grade surrounded by bar ren rock gave a series of readings like this relative readings background in country rock 2 10 inches from ore starting to rise to 3 5 inches away reading 75 3 inches away reading 1 inches away reading flat reading of thru ore and to ay 1 4 inches below then dropping off like it climbed the tube had a 3 inch active length there is no obvious way to determine either i the thickness or grade of the high grade seam the only thing that could be said in this case is that there was perhaps 2 to 3 inches of marketable ore however the point where one could say it is marketable can only be deter mined by the cost of opening a drift or of sufficient size to reach the seam in relation to the value of the ore more work needs to be done in order to clarify this relationship particularly where the ore is thin or varying rapidly in value at the moment all that can be said as a rule of thumb is to be extremely careful of evaluate mg ing ores where the distance the pr probe obe reading stays constant is less than 8 inches particularly if it rises sharply to its maximum value in this case deduct the width of the geiger tube from the 1 length of the hat flat top but con sider that there probably is only a very narrow seam over 8 inches to 20 inches the survey must be an analyzed carefully over 20 inches the readings should sh be reliable in any case where an important decision is to be based on a nar row seam scam the seam should be very slowly and carefully surveyed with readings taken very close together and the data analyzed by competent geologists to be sure that development would be justified |