Umuna Au Ag Prospect

The Umuna Prospect is a significant gold deposit with 5.7M oz's of Au identified from which 4.0M oz's of Au has previously been extracted and 1.6M oz's is currently in resource. The Umuna Prospect is classified overall as a Base Metal Carbonate Style deposit but on a detailed basis also shows features of Skarns and Epithermal Style mineralisation.

Gold was discovered on Misima Island in 1888 and by 1889 parties of men were working in the northern, eastern and southern flanks of Mount Sisa. Copper mineralization was discovered on Mount Sisa but was not worked. Total production from the underground workings from 1888 to 1942 is estimated to have been approximately 236,000 ounces.

Transporting ore from the Umuna mine circa 1904 

Transporting ore from the Umuna mine, circa 1904.

 

Cuthbert's Misima Gold Mining Company 

 Cuthbert’s Misima Gold Mining Company operations, 1935

 

Placer Dome became involved in Misima in 1985 and with an intensive focussed exploration program delivered detailed studies in 1987 that suggested a viable operation could proceed. The  Misima timeline is shown below:

  • 1985 -  Intensive Exploration

  • 1988 – Misima Mine construction commenced

  • 1989 – Official opening by PM Rabbie Namaliu

  • 1992 – Production reached 1 million ounces of gold

  • 1995 – Production reached 2 million ounces of gold

  • 1999 -  Production reached 3 million ounces of gold

  • 2001 – Mining from open-pits ceased

  • 2004 – Milling of ore ceased - 3.76 million ounces gold produced

  • 2005 – Deconstruction completed

  • 2012 – SML Rehabilitation and Relinquishment achieved (April)

     

    An overview of the historic Misima Umuna Operation is shown below.

Misima Umuna Ops image 

The Umuna Au Ag Prospect comprises numerous types of mineralisation including breccia, stockwork, vein swarms, replacements and fracture networks hosted with within greenstone, schist and granodiorite porphyry. The zone has been intensively explored and exploited over a 3 km long zone within which widths vary from 10 to 200 metres wide. It has been drilled to over 450 plus metres with good results. Extensions of the major controlling Umuna structure have now been identified over an additional 3km length. Oxidation extends to more than 300 metres depth in the central zones. Ore is free milling in oxide and sulphide with good recoveries. Umuna is complexly zoned from a geochemical and alteration perspective.

 

Geological Survey Mapping 1974

The schematic geology of the area where the previous production was extracted is shown below in plan and cross section.

 Schematic Geology of the Umuna Prospect

 

Schematic Geology of the Umuna Prospect

 

 Cross Section through the Umuna Prospect

Cross Section through the Umuna Prospect

Graphical representation of the distirbution of gold within the Umuna Zone from blast hole data is shown below.

 graph rep of gold image

Graphical representation of the distirbution of silver within the Umuna Zone from blast hole data is shown below.

 graph rep of silver image

Graphical representation of the distirbution of copper within the Umuna Zone from blast hole data is shown below.

 graph rep of copper image

Acquisition of the Misima Mines Pty Ltd Database in late 2012 which included surface sampling (11,846 soil, 2,941 rock, 4,853 trench and 25,980 channel samples, 2,640 exploration drill holes, 467,316 blast holes, drill core photographs, mine feasibility documentation, petrological data and production records, and survey data) allowed WCB to validate, compile and audit this data with the assistance of suitably qualified professionals whose careers have a history with the Misima Project and the Placer Pacific (ASX) / Placer Dome (TSX) Quality Control / Quality Assurance Protocols and Procedures including database development and design, resource modelling and reconciliation.

Following this process the Umuna Mineral Resource Estimate was developed by Richard W Lewis of Lewis Mineral Resource Consulting Pty Ltd under the independent guidance and supervision of AMC Consultants Pty Ltd (AMC). The resource is constrained by geological and grade domains and is incorporated within a conceptual open pit with results being reported at an USD$1,100 per oz gold price. The initial inferred Mineral Resource is outlined in the announcement October 7, 2013.

Misima Gold Mine - A case study in the use of historical data for an updated Mineral Resource estimate:

 - Click here to view the Presentation

 - Click here to view the Research Paper

WCB is currently actively reviewing and assessing the opportunity with respect to the Umuna Prospect.

Subsequently, the resource was upgraded to Indicated Inferred on 7 May 2015 as shown below:

Deposit

Material

RECLASS

Cut-off
g/t Au

Tonnes
Mt

Gold
g/t Au

Silver
g/t Ag

Au
Moz

Ag
Moz

Umuna

Oxide

Indicated

0.37

4.2

0.71

11

0.10

1.6

Inferred

0.37

2.5

0.94

21

0.07

1.6

Primary

Indicated

0.45

32

1.1

4.3

1.2

4.4

Inferred

0.45

4.9

1.2

8

0.19

1.3

Total

Indicated

36

1.1

5.1

1.3

6.0

Inferred

7.4

1.1

12

0.27

2.9

 

In addition a potential exploration target of 10-20Mt @ 0.8-1.25g/t Au has been defined.

The mineral resources at Umuna are drill data limited.  Further drilling will increase the resource.