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Orocobre completes Phase III drilling at Cauchari

Published by , Assistant Editor
Global Mining Review,

Orocobre Limited (Orocobre) has provided the following update on the completion of drilling and pumping test activities at the Cauchari joint venture (JV) property located in Jujuy Province (Argentina).

The exploration programme is being managed by JV partner Advantage Lithium Corp. (Advantage Lithium) who hold 75% of Cauchari. Orocobre owns 33.5% of Advantage Lithium's issued capital and 25% directly in the joint venture.


  • Phase III infill drilling and resource conversion programme was completed at the end of 2018 with 26 holes drilled in Phase II and III. An updated resource estimate in 1Q19 is expected to bring current inferred resources into the Measured and Indicated categories.
  • Drilling in the deep sand unit at CAU26 and deeper drilling on the CAU12 and CAU13 platforms confirms a significant expansion in the unit thickness. CAU12 has intersected more than 249 m of sand dominated material. Drilling has also expanded the aerial extent of the unit. The deep sand unit remains open at depth, where holes were terminated in sand and interbedded sand units.
  • Brine analysis from CAU19 in the SE Sector averaged 611 mg/l lithium and 4483 mg/l potassium in the deep sand beneath the upper sequence of evaporites and finer grained sediments which averaged 427 mg/l lithium. Brine sample results are pending for CAU26, CAU12 and CAU13.
  • The CAU11 30 day constant rate pumping test was completed on 24 November (see ASX announcement dated 28 November). The test was carried out at an average pumping rate of 18.4 l/s with the lower part of the well screened in the deep sand unit. Brine samples collected during the pumping test indicate that lithium and potassium concentrations remained constant throughout the test and averaged 512 mg/l lithium and 4735 mg/l potassium.
  • The CAU07 30 day constant rate pumping test continues in the NW Sector at a rate of 22 l/s. Brine sample results from the first seven days averaged 647 mg/l lithium and 4980 mg/l potassium with a Mg/Li ratio of 2.2:1, with final results expected end of January 2019.
Orocobre Managing Director and CEO Mr Richard Seville commented: "We are very pleased to have completed the Phase III drilling programme at Cauchari and commenced the engineering for the Feasibility Study. The Phase III drilling programme has successfully extended the footprint of the resource area to the south and at depth. Updating the resource estimate is expected to bring resources into Measured and Indicated categories in 1Q19. The thick sand sequence intersected by the recent drilling is very significant and shows a similar geology to the deeper holes drilled at Olaroz in recent years."


Drilling update

The Phase III drilling programme has been completed with some of the deepest holes drilled in the Cauchari-Olaroz basin to date, reaching a maximum depth of 617 m in CAU26, with the deep sand unit present at that depth. Drill hole CAU19 was completed in the southwest of the SE Sector to a depth of 519.5 m. This hole intersected the deep sand unit from 434 m to 519.5 m (a thickness of >85 m), with sandy units continuing at the end of the hole. The extent of the deep sand unit is further defined by intersections in drill holes CAU11, CAU12, CAU13 and CAU26. In CAU12 the deep sand unit extends over more than 249 m vertically, beginning at 360 m below the surface and continuing to the end of the hole at 609 m.

Brine samples from CAU19 in the deep sand unit averaged 611 mg/l lithium and 4483 mg/l potassium with a Mg/Li ratio of 2.1:1, while the lithium concentration in the overlying evaporite and clay sequence averaged 427 mg/l over a 300 minterval. Confirmation of the deep sand unit's substantial thickness and the elevated brine concentration found in CAU19 are excellent results. Brine sample analysis is pending for CAU12, CAU13 and CAU26. Drilling has confirmed the positive characteristics of the deep sand unit in terms of both porosity and permeability for future extraction.


CAU25 was drilled in the north of the SE Sector, north of CAU22. CAU25 intersected a sequence of clay, halite and interbedded fine sand units to a depth of 427 m. Brine sampling returned an average concentration of 497 mg/l lithium and 4045 mg/l potassium from 169 m to 345 m depth, with a low Mg/Li ratio of 2.6:1.

CAU26 is located in the southern region of the SE Sector and successfully intersected the westward extension of the deep sand unit.

Drill holes CAU12 and CAU13 were deepened to determine the thickness of the deep sand unit, as previous drilling at these sites had only intersected the upper part of the unit. This new drilling has confirmed a thickness >249 m in CAU12, and a thickness >100 m in CAU13 with both holes terminated in the sand. The deep sand unit appears to have favourable porosity and permeability characteristics. Core samples are currently being analysed for drainable porosity and other physical parameters in the GSA laboratory in the US. The deep sand unit appears to constitute an important source for future brine production in addition to the sands and gravels of the NW Sector of the project.

Pumping tests

The 30 day constant rate pumping test has been completed on test production well CAU11 in the SE Sector. This test was performed at a pumping rate of 18.4 l/s with a constant drawdown of 25 m in the pumping well. Water levels were also measured in a network of surrounding observation wells completed to different depths relative to the deep sand unit. Brine concentrations were monitored throughout the test. The brine concentration averaged 512 mg/l lithium and 4735 mg/l potassium throughout the test with a Mg/Li ratio of 2.6:1, confirming the results of the 48 hour pumping test conducted in February 2018 (see ASX announcement dated 6 March).

The 30 day constant rate pumping test in CAU07 is underway in the NW Sector and will be completed in mid-January. The pumping test is carried out at a rate of 22 l/s with a drawdown of 40 m. Assays received for the first seven days of the test averaged 647 mg/l lithium and 4980 mg/l potassium, with a Mg/Li ratio of 2.2:1. The CAU07 pumping rate is limited by well construction constraints and higher pumping rates are expected in future production wells based on the observed aquifer conditions. Brine samples are collected at regular intervals during the test and complete analyses are expected by the end of January 2019. The tests provide additional information on aquifer characteristics as an input to the three-dimensional groundwater model that is being developed to estimate lithium reserves and to develop a production schedule for the project. The pumping tests also confirm the minimum pumping rate to be expected for production pumping wells, in line with the company's previous expectations.

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