Summary:
The Caval Ridge Mine (CVM) includes two pits: Horse Pit and Heyford Pit.
The CVM is situated on the western limb of the northern Bowen Basin at the southern end of the Collinsville Shelf. The Permian coal measures in the region dip east at three to six degrees. Seam splitting is common at CVM, specifically in the Horse Pit area, and results in local steepening of the coal seam dips. Structurally there is one major fault in the north of Horse Pit and some minor associated faulting.
Economic coal seams occur in the terrestrial Moranbah Coal Measures (MCMs) and consist of approximately 300 m of labile sandstone, siltstone, mudstone, tuffaceous claystone and coal. Underlying the MCMs is the German Creek Formation: a marine influenced formation with quartzose to labile sandstone, siltstone, mudstone and thin coal seams. Overlying the MCMs is the Fort Copper Coal Measures that are characterised by thick uneconomic banded coal seams and tuffaceous sediments.
Remnant Tertiary basalt flows occur in the north of the Horse Pit. Elsewhere, Quaternary sands and clayey sands up to 30 m thick overlay the Permian sequence.
The targeted seams at the CVM and the Horse Pit include all seams that comprise the MCMs exceeding 40 cm in thickness. The primary seam targets at Horse Pit are the Q seam to P seam, the Harrow Creek (H) group of seams, and the Dysart (D) seams. All seams greater than 40 cm are determined to be targets for coking coal production. Seam nomenclature is based on the seam position relative to the ‘P Tuff’, a regional sedimentary marker (1 – 2 m thick). The seams at CVM are:
Q seam
Comprises several coal intervals modelled as Q01, Q02, and Q03. Throughout CVM, the Q seam is a full seam (Q01), splitting into Q02 and Q03.
P seam
Splits from a single seam in the south into several plies northwards. The major units are modelled as P02, P07, and P08, so named due to the association with the P Tuff that is consistent through this part of the Bowen Basin.
Harrow Creek Seam
At CVM, H16 is present along with seam splits H162 and H161 while H15 is missing but substituted by its lowest splits H06, H03, H02 and H00.
Dysart Upper seam
Fully coalesced and is modelled as D47, but it splits into multiple units at both ends of the ML. At CVM, D47 splits to D43, D40 and D45. D43 and D40 are largely shaly while D45 is often less than 0.3 m thick
Dysart Main seam
Three (3) major splits (D13, D121 and D02) exist over most of Horse Pit. Frequent splitting and coalescing occur including in the north of Horse Pit where the DL seam sits within 30 cm and is modelled with the D02.
DL seam
A consistent 60 cm band occurs under the D02 throughout most of CVM. Two additional coaly bands sitting below the DL have been identified and modelled: DLL (approx. 20 cm thick) and DLLL (10-20 cm thick).
D00 & C01 seams
Two additional horizons below the D02 seam were identified as D00 and C01 seams. D00 seam is located approximately 20 m below D02. It averages 1 m thick but reaches a maximum of 2.0-2.5 m in places. At this time, initial quality results indicate a high ash coal and poor yielding seam. C01 occurs 50-55 m below the D02 and is about 1 m thick. It has only been logged in stratigraphic chip holes, no quality data is currently available for the C01. D00 and C01 seams are not planned to be targeted by mining at CVM or the Caval Ridge Mine Horse Pit Extension Poject.