1971 Monthly reports, maps & drill logs for AP 2677 Walbiri Prospect

Abstract

During the month geological field work continued on the Walbiri Prospect in AP 2677, detailed mapping in the Djuburula AP on the southern flank of the Patmungala Sync line and with trenching and pitting on the Walbiri Prospect. Field activities were suspended on the 5th December and the camp at Wanabi was moved to Alice Springs. Since then, the equipment and vehicles have been inspected so they can be repaired or replaced if necessary for 1972. Geological maps are being drawn in preparation for detailed geological reports of individual prospects. Those maps completed to date are included in this report. AP 2677 - YUENDUMU MINING COUNCIL 1st June, 1972 Geological mapping using enlarged aerial photographs (1:10,000) continued in the vicinity of the Walbiri Prospect in the eastern portion of the authority area. In November it was reported that four mineralized horizons occurred within the broad mineralized zones. Six geological cross-sections have been drawn and are included in the report. Datum for all the sections was a siliceous sandstone marker horizon on the southern side of the mineralization. Correlation between the sections is sometimes difficult because of frequent lateral changes in lithology. A brief summary of the lithology of the mineralized horizons is as follows: Horizon 1 - Composed of coarse-grained arkosic sandstone and is continuous for about 2.8 m. Only three high radioactive spots have been found, earth of which was 2,000 cps but along the horizon the radioactivity is at least twice background, that is about 80-100 cps with several spots of 100-200 eps. Horizon 2 - This occurs on the western end of the mineralized zone and has a length of about 1km. Composed of medium to fine-grained arkosic sandstone. Anomalously high radioactivity is found in several spots and carnotite was found in four separate places. Three trenches of Group A have been dug across this horizon. Horizon 3 - Composed of coarse-grained arkosic sandstone with minor medium-grained sandstone. It is about 600m long and 20m wide. Anomalous radioactivity was found in several places and carnotite was found in five places. Seven trenches and pits of Group B were dug across this horizon.

Horizon 4 - The host to the mineralization is a coarse-grained arkosic sandstone about 15.20m wide with interbeds of medium-grained arkosic sandstone. At the base of this unit is a bed of silicified sandstone. is 800 m long with carnotite being found in five places. Trenching was only carried out in mineralized horizons 2 and 3 because both 1 and 14 were inaccessible. The maps included with this report show the geology, radioactivity and distribution of the carnotite mineralization in these trenches. It has been found that the carnotite has four modes of occurrence 1: Associated with fracture zones, 2: Associated with ferruginous material, 3: Associated with clay pellets within the sandstone. It Disseminated in the sandstone filling interstices within the rock. Information is to hand for the trenches completed in the mineralized horizons 2 and 3. Trench A1 is 114m long; .8m wide and 12m deep. Carnotite occurs associated with ferruginous material as well as in joints and in the matrix of the rock. Trench A2 is located 40m west of A1 and is 29.5m long comprising three individual trenches. Carnotite is found associated with ferruginous material and in joint or fracture planes. Trench A5 is located 32m east of A1. This trench was not satisfactorily completed before the end of the field season. No mineralization was found in this trench. Radioactivity in the trench only averaged about 50 cps (background). Trench B1 is a pit 12m deep. Surface radioactivity is 1,000 cps and did not increase with depth. Carnotite occurs in the bottom part of the hole associated with a fracture, ferruginous material and with clay pellets. The rock is coarse-grained arkosic sandstone. From the surface to 0.5m deep carnotite occurs only in trace quantities while it comprises three to five percent of the total rock in the bottom meter. Trench B2 is 2.5m long; 0.9m wide with a maximum depth of 0.9m. Highest surface reading was 5,000 cps and this increases to 6,500 cps in the trench. Abundant carnotite (up to 5% of the rock) is associated with fractures and in the matrix of the rock which is a siliceous fine-grained arkosic sandstone. Trench B3 is a pit, depth 0.8m; surface radioactivity 4,500 cps down to 1,000 cps in the trench. Carnotite (about 1-5% of total rock) occurs in and in the matrix of the rock which is a fine-grained siliceous sandstone. Trench B4 is a pit, depth 0.7m; surface reading 1,000 cps up to 1,500 cps in the pit. Carnotite (1-2%) is associated with fractures. Rock type is a medium-grained arkosic sandstone. Trench B5 has a length of 6.4m, a depth of 0.8m with the highest surface reading being 5,000 cps increasing to 7,000 cps with depth. Carnotite (trace to 1-%) is associated with ferruginous material and clay pellets in a very coarse-grained arkosic sandstone. Trench B6 is 5m long; 0.9m deep, with surface radioactivity of 1,500 cps increasing with depth to 10,000 cps. Carnotite (trace to 3-5%) is associated with fractures, ferruginous material and filling interstices in a coarse-grained arkosic sandstone with a thin bed of fine to medium-grained sandstone. Trench B7 is a pit, depth 1m, surface radioactivity 1,200 cps increasing to 2,000 cps in the pit. Carnotite (up to 1-2%) occurs in fractures with ferruginous material and in the interstices of the rock. Coloured aerial photographs have been received for the outcropping rocks on the northern margin of the Ngalia Basin. These will be used to provide a base map for the 1972 field season.