COMMONWEALTH OF AUSTRALIA DEPARTMENT OF NATIONAL DEVELOPMENT BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS RECORD No. 1963/114 0111329 4- NARROMINE AND BATHURST AIRBORNE MAGNETIC AND RADIOMETRIC SURVEYS, NSW 1961 by G.A. YOUNG The information contained In this report has been obtained by the'Department of National Development, as part of the policy of 'the Commonwealth Government, to assist in the exploration and development of mineral resources. It may not be published in any form or used in a company prospectus or statement without the permission in writing of the Director, Bureau of Mineral Resources, Geology and Geophysics. si
Transcript
COMMONWEALTH OF AUSTRALIA
DEPARTMENT OF NATIONAL DEVELOPMENT
BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS
RECORD No. 1963/114
0111329 4-
NARROMINE AND BATHURSTAIRBORNE MAGNETIC AND
RADIOMETRIC SURVEYS,NSW 1961
by
G.A. YOUNG
The information contained In this report has been obtained bythe'Department of National Development, as part of the policyof 'the Commonwealth Government, to assist in the explorationand development of mineral resources. It may not be publishedin any form or used in a company prospectus or statement withoutthe permission in writing of the Director, Bureau of MineralResources, Geology and Geophysics. si
COMMONWEALTH OF AUSTRALIA
DEPARTMENT OF NATIONAL DEVELOPMENT
BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS
RECORD No. 1963/114
NARROMINE AND BATHURSTAIRBORNE MAGNETIC AND
RADIOMETRIC SURVEYS,NSW 1961
Pr
by
G.A. YOUNG
The information contained in this report has been obtained bythe Department of National Development, as part of the policyof the Commonwealth Government, to assist in the explorationand development of mineral resources. It may not be publishedin any form or used in a company prospectus or statement withoutthe permission in writing of the Director, Bureau of MineralResources, Geology and Geophysics.
I.
%
CONTENTS
SUMMARY
Page
1. INTRODUCTION 1
2. GEOLOGY 1
3. INTERPRETATION 3
4. REFERENCES 7
APP:CNDIX - Operational Details
ILLUSTRATIONS
Plate 1. Locality map^ (Drawing No. I55/B1-16)
Plate 2. Total magnetic intensity profiles; Narromine, NSW.^(I55/B1-6)
Plate 3. Total magnetic intensity prollles and geology;^(I55/B1-4)Narromine,
Plate 4. Total magnetic intensity profiles; Bathurst, NSW.^(155/B1-5)
Plate 5. Total magnetic intensity profiles and geology;^(I55/731-3)'Bathurst, NSW.
Plate 6. Radiometric results and geology; NaTromine, NSW.^(I55/31-1T)
Plate 7. Radiometric results and geology; Bathurst, NSW.^(155/31-15)
SUMMARY
An airborne magnetic and radiometric survey of the majorparts of the Narromine and Bathurst standard map areas was flown duringthe perioei October '6o December 1961. The operations are describedand an analysis is made of the magnetic and radiometric results.
The results show that considerable correlation exists betweenanomalous magnetic trends and known geological structure. Thiscorrelation indicates that the aeromagnetic data will provide valuableinformation on the regional geology in areas of alluvium cover. Thedata may also be expected to delineate areas amenable to a more detailedsearch for metalliferous deposits.
1963/ 1 14
1. INTRODUCTION
At the request of the Department of Mines, New South Wales,a programme of airborne magnetic and radiometric surveys was commencedby the Bureau of Mineral Resources, Geology and Geophysics in 1957with the object of assisting in the search for mineral deposits andproviding information related to problems of regional geologicalstructure. The areas selected for survey are known to containmetalliferous deposits; some have considerable areal extent of soilmantle obscuring the rock surface. The Bureau of Mineral Resources hasso far completed airborne surveys of the following standard map areas(scale 1%250,000):
Cobar, Nymagee, and Cargelligo (Spence, 1961)
Bourke and Forbes (Carter, 1960)
During October to December 1961, a further stage.in theprogramme was completed with the flying of the major parts of theNarromine and Bathurst standard map areas (scale 1:250,000).
some previous geophysical work has been done in the Narrominean Bathurst areas. The airborne magnetic and radiometric survy ofForbes standard map area (Carter, 1960) was extended to include thesouthern part of the Narromine standard map area and the western partof the Bathurst standard map area.
The discovery of uranium minerals in the Carcoar districtstimulated a series of ground radiomF:tric surveys by the Bureau ofMineral Resources (Daly, Dyson, and Pearce 1951; Matheson, 1952;Daly, 1955) and by the Department of Mines, New South Wales (Raynerand Ralph, 1954).
The Bureau of Mineral Resources made further ground surveysin this area during 1955 using magnetic, electromagnetic, self-potential,and geochemical techniques (Horvath arql Rowston t 1957)-
Results from this work indicate that in the Carcoar districtradioactivity is associated with slate near its contact with a hornblende-diorite intrusion, and magnetic anomalies of intensity ranging from 250to 2000 gammas are associated with the hornblende•diorite igneous mass.It also appears that troughs of low magnetic activity in the area of thehornolende-diorite mass outline major shears. The diorite dykes crossingthe area show no appreciable magnetic influence.
2. GEOLOGY
Regional geological maps of the Narromine and Bathurst standardmap areas shown in Plates 3 and 5 are based on information supplied bythe Department of Mines, New South Wales and the Department of Geologyand Geophysics, University of Sydney.
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Palaeozoic sediments and metasediments, extensivelyintruded by granite, comprise the geology of these areas. Silurianrocks, consisting mainly of quartzite, sandstone, Shale, and slate,form the larger part cf the Palaeozoic outcrops. They overlie theOrdovician rocks, which are mainly shale and slate with some andesiteiquartzite, and chert. These Ordovician rocks have been subject: toconsiderable folding and, in some areas, considerable regional andlocal metamorphism.
Ordovician outcrops are in the form of ill-defined meridionalbelts which alternate with Silurian or younger beds or are separated byigneous intrusions, the Silurian rocks being preserved for the mostpart in north-trending synclines.
Devonian sandstone, quartzite, and volcanic rocksunconformably overlie the Lower Palaeozoic beds north-east and north-west of the Bathurst area and in the southern part of the Naxromine area.
Narromine area
The geology for most of this area is not well known owingto an extensive alluvial cover, particularly in the north. Moderateigneous activity which occurred during, and prior to, Middle Devoniantimes is the main soul'oe of mineralisation in this area. The mostextensive igneous outcrop extends southwards from Narromine to east ofParkes.
West of this igneous mass, gold has been mined in the PeakHill district (Anderson, 1890), the mineralisation occurring as pyriticquartz reefs in Silurian slate. A considerable quantity of alluvial goldhas also been mined in this locality.
In the region about Trundle bauxite has been derived from thelaterisation of a felspathic rock, probably a tuff. (Hanlon, 1944).
Except for these minerals and gold obtained from the Tottenhamdistrict, few ore deposits of economic significance have been located inthe Narromine area.
North and east of the Narromine area, Jurassic rocks areexposed, these being mainly sandstone,
Bathurst area
The area was subject to many periods of igneous activityduring the Palaeozoic era, the first period of major importance occurringat the end of the Silurian. Mineralisation att:?ibuted to this Bownirsepoch of granitic intrusion are the gold at Truney and Rockley and thecopper at Cow Flat (Browne, 1949).
The Kanimblan igneous epoch at the close of LowerCarboniferous times produced the majority of the plutonic rocks nowexposed in this area. The most notable is the Kanimblan batholith,mainly composed of biotite granite, which extends from Hartley throughRydal, Oberon, and Bathurst, towards Orange and Newbridge.
Associated with these intrusions is a wide variety of mineralswhich are of economic importance including the gold, silver-lead, andiron ores of Hill End, Orange, Bathurst, Blayney, and Lyndhurst and themolybdenum of Yetholme (Browne, 1949).
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Mineralisation occurs in many places as contact metamorphicdeposits, the invaded rocks being entirely pre-Carboniferous andpredominantly Silurian. Such deposits are the molybdenum and tungstenores at Yetholme, and the chalcopyrite at Bathurst, Molong, and Cadia(Voisey, 1953).
At Cadia and Carcoar small iron orebodies appear to bemetasomatic replacement deposits consisting mainly of haematite,limonite, magnetite, and manganese oxide in Silurian slate (David, 1950).
Uranium ores of torbernite, autunite, and uraninite associatedwith cobalt ores have also been found at Carcoar (Rayner and Ralph, 1954).This mineralisation is found in zones of shearing in an environment ofinterbedded sedimentary and volcanic rocks, probably Silurian, adjacentto an intrusive diorite mass.
Silurian rocks are also the host rocks for mineralisation atHill End where auriferous saddle reefs occur as fissure fillings(Voisey 1953, Harper 1918).
A large part of the area west and south of Bathurst is coveredby Tertiary basalt which contributes to the Central Highland plateausurface and has preserved deep leads in the Orange, Lucknow, Bathurst,and Rockley localities, which were worked for tin and gold (Voisey, 1953).
3. INTERPRETATION
Magnetic
Magnetic results from the Narromine and Bathurst standard mapareas are given in Plates 2 to 5. Total magnetic intensity profilesproduced by a low-sensitivity curvilinear recorder have been adjustedto an exact overall scale of 1:250,000 by controlling the positions ofthe flight traverse lines at the eastern and western boundaries of thesurvey areas. These profiles are drawn with a probable error of- 100 gammas and are presented solely for descriptive purposes in thisRecord.
Plates 2 and 4 show the magnetic profiles related to idealisedgrids of flight traverse lines in the Narromine and Bathurst ay..eas. Thesegrids, for convenience of presentation, have scales of 1:250,000east-west and 1:62,500 north-south. Plates 3 and 5 show every fourthprofile superimposed on regional geological maps of the survey areas.The probable error in positioning this magnetic data is estimated to be
+- 4 mile east-west and - mile north-south.
Narromine area. The magnetic profiles shown on Plates 2 and 3indicate the correlation that exists between anomalous magnetic trendsand regional geological structure in this area. The magnetic disturbanceis mainly associated with Silurian rosks, anomalies being generallyelongated in a direction trending N10 W, which reflects the regionalgeological strike. This general magnetic trend differs from that observedto the south in the Forbes standard map area (seale 0 1:250,000) whereanomalies are elongated in a direction trending N30 E (Carter, 1960,Maps G324-8, 9, 11, 12), but is similar to those observed in the Cobarand Nymagee standard map areas (Spence, 1961 9 Maps G290-3 9 4 9 5 9 6 andG338-5, 6, 7, 8).
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Many anomalies have a very limited east-west extent and apronounced north-south elongation which occasionally exceeds 20 miles.Such anomalies, for example those about Narromine, have a form generallyassociated with near-surface vertical tabular bodies commonly prodUcedeither by mineralisation along shear zones or by dykes. Spence (1961)reports similar anomalies in the Cobar standard map area and postulatesthat they may mark shear zones similar to that which runs through 'Cobar.
Another form of magnetic disturbance occurs in the area westof Peak Hill and extends southwards into the Forbes standard map area(Carter, op.citl:Map G324-9). The disturbed zone, which has an east-westextension of approximately 15 miles, is characterised by anomalies of acomplex nature whose amplitudes rarely exceed 500 gammas and whose formsindicate their sources to be near surface level. The anomalies originatefrom Silurian rocks. Linear magnetic trends located on the eastern flankof the zone correspond to outcrops of Silurian volcanics. In the regionabout Parkes, similar anomalies (Map G324-9) correspond to outcrops ofintrusive and extrusive andesite, which are associated with theauriferous mineralisation of the Forbes-Parkes gold field (Andrews, 1910).
Another magnetic zone, located 15 miles S40 °W of Narromine,indicates a northerly continuation of the Silurian rocks at a shallowdepth beneath the alluvium cover and may also indicate further areas ofauriferous mineralisation.
The region of greatest magnetic disturbance is that situated westof the granite outcrop of the Gobondry Mountains. From the limitedgeological information available, the sources of the loealised anomaliespossibly lie within Silurian rocks. Similar anomalies have been observedin the south-eastern part of the Cobar standard map area (Spence, 211..cit.,Map G290-6) over outcrops of serpentine. It is possible therefore thatthe anomalies west of the Gobondry Meeatains are related to the occuErenceof serpentine, and the intense isolated anomaly lccated 12 miles 550 W ofTottenham probab3y has a similar source. These areas of intense magneticdisturbance lie in a zone trending N30 W $ paralleling the general trendof the individual anomalies.
Slight magnetic activity was recorded over the main graniticmass of the Gobondry Mountains. However, the periphery cf the granite isdefined by anomalies of about 300 to 400 gammas, whioh may arise frommagnetic mineral eoneentrations. These anomalies are considered towarrant further investigation. A high-grade haeme .6ite deposit in highly-altered sedimentary rocks (slate, epidote, and marble) is known to existalong the eastern boundary of the granite (Griffin and Wynn, 1961).
The north-eastern part of the Narromine standard mttp areaincludes the southern margin of the Coonamble Basin. Hower, most ofthe anomalies here indicate that the magnetic basement is very closeto the surface and nowhere is the estimated thickness of sedimentsgreater than 1500 ft.
Bathurst area. The magnetic profiles presented in Plates 4 and 5show correlation between the anomalous magnetic trends and the regionalgeological structure. To some extent, Plate 5 also indicates correspondenceof magnetic anomalies with known areas of mineraJisation.
The magnetic anomalies appear to be associated with Ordovicianrocks, are7.s of disturbance having a distinct northerly extension whichreflects the regional geological strike. The northerly elongation oflocalised magnetic anomalies common in the Forbes and Narromine standardmap areas is not so apparent in this area. Slight magnetic activity isassociated with Silurian or Devonian rocks; outcrops of Devonian volcanicsnorth of Bathurst show no magnetic activity.
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Although magnetic disturbance is apparent in various degreesthroughout almost the entire area, the more intense magnetic anomaliesare mainly confined to the region defined by the townships of Molong,Canowindra, Cowra, Blayney, and Orange. Within this area many intrusiveand extrusive rocks have been mapped (1:';tevens, 1948 and 1950)^•Ordovician andesite and Tertiary basalt appear to be predominantly: thesources of the magnetic anomalies. Stevens places the andesites in theLower Silurian (Cargo Andesite Series) and notes the presence oftrachyandesites and basalts in the series. The magnetic anomaliesassociated with these rocks are similar to those recorded over outcropsof andesite in the Forbes-Parkes gold field (Carter, 1960, Map G324-9;Andrews, 1910).
North of Woodstock, the north-trending fault (Stevens, 1948and 1950) which marks the contact of the andesitic rocks with youngerstrata is reflected by changes in the character of the magnetic profiles.An area of limestone exposure (Stevens, 1948) located seven miles westof Black Rock Range (shown in Plate 5 as occurring in Ordovician outcrops)typically show no magnetic disturbance. Outcrops of quartz porphyry andgranite west of the fault have no associated magnetic anomalies.
The periphery of the granitic mass located south of Woodstockis defined by magnetic anomalies of amplitudes ranging up to 600 gammas.It is possible that these anomalies result fr.m contact metamorphism andassociated mineralisation, but they may be related ta exposures ofaadesite about the intrusion. No magnetic anomalies are associated withthe granite or Ordovician rocks exposed east and south-east of Woodstock.
An intense magnetic anomaly at Cadia probably corresponds tomineralisation produced by a monzcnite intrusion. Iron ore depositsassociatsd with this intrusion (Griff‘La and Wynn, 1961) contain magnetiteand are the probable source of the intense magnetic anomaly. In otherareas of known iron mineralisation 2 viz Woodatock v Blayney, Orange, andCarcoar (Griffin and WYnn, op. cit), no similar anomalies were observedwhich may be due . either to the small size of the 012e -bodies or to the i7:onbeing mainly in the form of haematite.
Slight magnetic disturbance is apparent in the area of graniticoutcrop betgeen Carcoar and Blayney. The western boundary of the intrusionis defined by magnetic anomalies apparently associated with the Ordovicianrocks, East of the intrusion similar anomalies are recorded in a regionof Ordovician outcrops but the eastern boundary of the intrusion is notdelineated. Magnetic anomalies in the area of a reported hornblende-diorite outcrop (not shown) at the southern extremity of this intruson(Plate 4, Flight-lines 45 and 46, longitude 1490091) have amplitudesranging up to 500 gammas. This intensity accords with anomaly amplitudesof 2000 gammas measured in the ground magnetic survey (Horvath and Rowston,1957).
Slight magnetic disturbance is associated with the main mass ofthe Kanimblan batholith about Bathurst. To the south, intense anomaliesappear to be associated with the Ordovician rocks. The character of theseanomalies is similar to that of the Canowindra locality and may thereforerepresent another northerly-trending belt of rooks with a high andesitecontent.
kt the southern boundary of the survey area, due south ofBlayney, a pronounced linear magnetic trend is defined. It is similarin character to those occurring in the region about Narromine. Thegeological significance of this anomaly is unknown.
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Radiometric
Radiometric results from the Narromine and Bathurst areasare presented in Plates 6 and 7. Profiles of radioactive intensityrecorded by the inboard scintillograph have been adjusted to an exactoverall scale of 1:250,000, using a process similar to that adopted forthe preliminary profiles of total magnebic intensity. Plates 6 and 7present the radioactive profiles recorded on alternate lines,superimposed on regional geological maps of the two survey areas. Areaswhere the radioactive intensity level increases significantly areindicated on these plates.
Discrete radiometric anomalies, assessed from both the inboardand outboard scintillographs as resulting from localised sources, are alsoshown on these plates.
The prot.bable error in positioning of this radiometric data isestimated to be -*mile east-west and ± -1- mile north-south.
Narromine area. The radiometric profil.as on Plate 6 show thatareas of increased level in radioactive intensity are elongated in anortherly direction and are predominantly associated with areas of igneousoutcrop. Two such areas are those located about the Gobondry Mountains,and the Sappa Bulga and Herveys Ranges, both areas corresponding tooutcrops of Ordovician granite. A third area is that located eastof Peak Hill, which lies on the extension of the axis of the Forbes-Parkesgold field, and may therefore indicate the presence of andesite in thislocality.
Four radiometric anomalies were recorded and their positions areshown in Plate 6. The amplitude of these anomalies is not large; a groundinvestigation will be necessary to complete the assessment and determinethe source of the anomalies.
Radiometric results illustrated south of Flight-line 63 arebased on data from a 1;revious survey (Carter, 1960).
Bathurst area.. Three localities where pronounced increases inthe level of radioactive intensity are evident are those about Bathurst,south and south-east of Woodstock, and northwards from Cowra. The mostnotable of these is that about Bathurst which corresponds to the exposureof the Kanimblan batholith. The area of increased radioactive intensityextending northwards from Cowra strongly reflects the regional geologicalstructure and is primarily controlled by exposure3of granite and quartzporphyry; the area to the south and south-aast of Woodstock is probablya southerly continuation of this although primarily controlled by graniteoutcrop.
In general, Ordovician rocks in the Bathurst area arecharacterised by low radioactive intensity, although one notable exceptionis apparent west of Blayney and Carcoar. This area shows a moderateincrease in radioactive level. At its south-eastern extremity groundradiometric surveys have shown uranium mineralisation to be associated withslate near a hornblende-diorite intrusion (Daly et al., 1951; Matheson1952; Rayner and Relph, 1954; Daly, 1955).
Nine radiometric anomalies were recorded; their positions areshown on Plate 7. The amplitude of these anomalies is not large; a groundinvestigeion will be necessary to complete the assessment and determinethe source of the anomalies.
