itt6t /23 PL./14,6)1A* 5exTv..4 ava DiRECTOR

COMMONWEALTH OF AUSTRALIA. Tj4 t Art I S 3

kl"

DEPARTMENT OF NATIONAL DEVELOPMENT.

BUREAU OF MINERAL RESOURCESGEOLOGY AND GEOPHYSICS.

RECORDS.

1 96 0/1 23

008840

RESULTS OF DIAMOND DRILLING BY BUREAU OF MINERAL RESOURCES, 1959-1960,AT THE CRATER LINE, NEAR BATCHELOR, NORTHERN TERRITORY.

by

J.M. Rhodes.

The information contained in this report has been obtained by theDepartment of National Development, as part of the policy of the Common-wealth Government, to assist in the exploration and development of mineralresources. It may not be published in any form or used in a companyprospectus without the permission in writing of the Director, Bureau ofMineral Resources, Geology and Geophysics.

RESULTS OF DIAMOND DRILLING BY BUREAU OF

MINERAL RES onCES: 2 13,527_1.90AT THE CRATER

NE NEAR BATCHELOR s NORTHERN_ TERRITORY..

by

J.M. RHODES.

RECORDS 1960/123

CONTENTS

PageSUMMARY^ 1

INTRODUCTION

DRILLING^ 2

DRILLING RESULTS^ 2

Radiometric Investigations^ 2

Mineralogical Investigations

CONCLUSIONS AND RECOMMENDATIONS^ 3

. REFERENCES^ 3

LIST OF PLA2ES,

PlateNo.^ Title^ s cale

1. Locality Map 1 inch = 10 miles1 inch =

2. Surface Map

3. Cross Section 24° north along BI R 1 inch = 40 feetDiamond Drill Hole No. lA

4. Radiometric Assays, Lithologicand Radiometric Logs. 1 inch = 10 feet

SUMMARY

DDH. No. lA was drilled to obtain unweathered corefor detailed investigation of the source of the radioactivityof conglomerate within the Crater Formation.^Mineragraphic,petrographic, and radiometric investigations indicate that theconglomerate contains less than 0.05% Th02, and that the radio-activity is due to the mineral thorianite, an oxide of thorium.UraniuM is present as a trace only.

The present demand for thorium is insufficient towarrant further investigation of these rocks.

INTRODUCTION

The Bureau of Mineral Resources Diamond Drill HolelA is situated about 1.4 miles east-north-east of the northernend of the main runway of Batchelor air-strip, 43 miles south-south-east from Darwin.

Pebble conglomerates of the Crater Formation havebeen known to be radioactive since 1952.^Three previous attemptshave been made to obtain information on the source of the radio-activity by diamond drilling.

In 1952, the Bureau of Mineral Resources drilledtwo holes 110 feet and 154 feet long at the Crater Prospecthalf a mile west of DDH. No.lA (Matheson, 1952: Dodd, 1953).The core recovery was low and the rock obtained was not fresh.Territory Enterprise Pty. Ltd. drilled three diamond drill holeswhich ranged from 100-feet to 250-feet vertical depth in theCrater Formation about 1-mile east of Batchelor. Slightly radio-active pebble conglomerate was intersected in two of the holes.No radioactive minerals were identified. In the same area aline Of waggon drill holes 25-feet apart and 20-feet deep con-firmed that the radioactivity was restricted to the pebbleconglomerate beds.^In 1955, Rio Tinto Finance and ExplorationLimited drilled in the Crater Formation immediately north ofManton Dam, 13 miles north-north-east of DDH. No, 1A. Threeholes were drilled all of which intersected radioactive con-glomerate. Although the intersections occurred at depths greaterthan 200 feet, the core was weathered and petrographic exam-ination failed to establish the source of the radioactivity(Rattigan, 1955).

The present hole was drilled to obtain unweatheredcore from the Crater Formation to ascertain the source of theradioactivity by detailed mineragraphic, petrographic andradiometric examinations.

Within the area selected for drilling, a planetable survey showed three conglomerate bands which occur withina stratigraphic thickness of about 30 feet (Plate 2). (Theconglomerate beds correspond to the No. 1 Pebble Bed of Dodds

The hole as designed with a bearing of 24° northand a depression of 70 to intersect the south-westerlydipping conglomerate beds about 500 feet below the surface.

-2 -

DRILLING

DDH. No. 1 was commenced in December, 1959, andabandoned in April, 1960, at a depth of 436 feet because ofunstable ground resulting in jammed casing. The three con-glomerate beds were not intersected. DDH. No.lA was thencommenced and was completed at 666 feet in July, 1960. Thishole is collared one and a half feet closer to the conglomerateoutcrop than DDH.No.1, and has the same bearing and depression.This hole was cased to 560 feet. The overall core recovery was83%.

DRILLING RESULTS

The three conglomerate beds were intersectedbetween 508 feet and 542 feet. The stratigraphic thicknessof this interval is about 23 feet (Plate 3) and the core re-covery between 508 feet and 543 feet was 51%.

Radiometric Examinations

Bore hole logging showed radioactivity between508 feat and 543 feet. The average grade over this intervalwas 00012% eU308 with a Maximum value of 0.04% eU3

0 3. Exam,-inations of the core showed that the high radioactivity isassociated with the three conglomerate beds (Plate 4). Thesmall peak of 0.012% eU708 between 520 feet and 523 feet couldnot be distinguished li-thologically.

Radiometric core assays were made from the wholeof the interval between 506 feet and 544 feet. Detailed com-parison of conglomerate samples with uranium and thoriumstandards showed that thorium is responsible for the radioactiv-ity. Plate L. shows assay results which exceed 0.02% Th02 or0.01% ell-40,^The eU.408. The elJ08 values which represent theamount o KdioactivIt, not contaIned uranium, are shown forcomparison with logging results.^The assay results whenweighted for length show that the average grade between 508 feetand 542 feet in DDH.No..1A is about 0.018% Th00; the averagegrade of the conglomerate alone is about 0.054% T11020

Mineralogical Investigations

Samples of the core were sent to the Bureau ofMineral Resources Canberra Laboratories for mineralogicalexamination by W.M.B. Roberts.

Examination with the X-ray spectrograph ofcrushed samples from the three conglomerate beds, and of theheavy residues of the crushed samples, showed that thorium wasthe only radioactive clement present in any quantity. A slighttrace of uranium was detected in the heavy residue of one ofthe samples (537 fact 6 inches to 5)41 feet 10 inches).

Microscopic examination of the heavy residuesshowed that the minerals present were zircon, rutile or anatase,iron oree, and a vitreous black mineral which was identified byX-ray diffraction as thorianite, an oxide of thorium.

A quantitive analysis by X-ray spectrogr,.phy onone crushed sample (511 feet 6 inches to 51)4 feet) showed it tocontain 0.040% Th02.

The quantity of uranium present was too small tobe determined accurately. It is probably of the order of0.002% U308.

7

pONCLTJqI.0,15S1\T _RECOMMENDATIONS,

Radioactivity within the three conglomerate bedsintersected in DDH.No.lA is due to the mineral thorianite, anoxide of thorium, which probably occurs in the matrix. It isconsidered that this feature can be applied to the CraterFormation as a whole. Because thorianite and other "heavy"minerals are associated with the conglomerate beds, it issuggested that those deposits are of detrital origin.

The conglomerate beds of the Crater Formation areextensive but very low-grade thorium deposits. No further in-vestigations are warranted.

p., EFER111. CES

Dodd, P.H., 1953^-

MacKaypN.J. , 1953^-

Matheson, R.S.,1952 -

Rattigan, J.H. 91955 -

Crater Line Investigations, Rum jungleNorthern Territory.74.-tect.B2.1r_salia,dtesour.to..Lt.. 1953/29

Crater Prospect (1951) Rum Jungle, Nor-thern Territory. aa.c...J3ur_.Min.,114.1sour.1953/28

Rum Jungle Progress Report to 30thS t amb or, 1952. R^injauourn..A.Lu,§Lt..1952/-?Report on Exploration Activities on Radio-active Pebble Conglomerates of the CraterFormation, Manton Area, Northern Territory,during 1955. Rio Tinto Finance andExploration Limited.

PLATE I

Scale.

0 MILE

N• DRILL SITE

0 Water Tower1\\ \

it

/' I

/I//

///I

//

//

LOCALITY MAPb.M.R DIAMOND DRILL HOLE NO I A

CRATER LINE,

NEAR BATCH ELOR, N.T.

NT 15-3Bureau of M/,-,era/ Reso,./Pcc,s;Geo/09y^Geo/ohysics,^44,./94../.574. /960.

Coarse quar/z greyfrvacke.

5 010 10 20 FT.

PLATE 4

Gr." 1‘ Sdr's,or7e, shale.

0.01

0 • 0 1.

0-02

0.02

0.03

0. 04

0.02.

Dep fh

5001

LITHOLOGICLOG

.t.

0-01

RA D IOMETR IC^LOG

ZeU3080.02 0.03

sot G11000

509^oo o000

511' ew -000000

514' 000

520'

525'

"o•..c000000

I.8325"000

-^537' 6"—z-,-8.

000.{

000541'10"

000

.^•^.

550'^•

Re ferernce

0000000000 n

Cor,dorp,ero Quar Z^yreykvacke

0.04

RADIOMETRICASSAYS

% eU308 70ThOz

• (1).'^(2)

10.02

0.040•02

(I) 1.1.5,r79 0308 (p0-chblencie) standard(2) Using Th 02 sy‘ohoiord.

Thor ic./er, respons;ble far roo//,ac v y

Scale,

RADIOMETRIC ASSAYS,

LITHOLOGIC AND RADIOMETRIC LOGS

lb.M.R. DIAMOND DRILL HOLE N9 IA

CRATER LINE, NEAR BATCHELOR, N.T.

Bureau ol 4/1/;..,era/ Resources, Geology anal Geophys/c.s,Dor vv/r7 , 4u.yus/. /960.

NT 15-6