Thank you for joining today's teleconference for the release of Mount Gibson Iron's March quarter activities report. Mount Gibson Chief Executive Officer, Peter Kerr, will be leading the discussion and is joined by Chief Financial Officer, Gillian Dobson, and External Relations Manager, John Forwood. Mr. Kerr will provide a brief overview, after which there will be an opportunity to ask questions. Due to time constraints, only institutional participants will be invited to ask questions at that time, and a recording of the call will also be made available via the Mount Gibson website shortly after completion of today's teleconference. Please go ahead, Peter.
Thanks very much, Luke. Morning, all, and thanks for joining us to discuss Mount Gibson's March 2023 quarter activities report. As usual, I'll give a brief overview and then hand back to Luke for any questions you may have. Overall, the March quarter reflected a good turnaround for the Koolan operation, with the processing plant return to full capacity at quarter end and shipment rates now increasing. This was despite the usual northern WA wet season constraints and, in particular, the impacts on our road transport and barging logistics as a result of the Kimberley mainland flooding events in January and February. The improved operational performance meant we generated solid positive cash flow, enabling the company to double its cash and investment reserves to just over AUD 83 million at quarter end.
At the same time, we further built our stockpiles of mined high-grade ore to 1.2 million tons ready for processing. This stockpile's worth over AUD 170 million at current prices once it's crushed for sale. In relation to Koolan Island in a bit more detail, mining activity was in line with forecasts, with ore production similar to the prior quarter at just under 1 million tons. Importantly, the waste to ore strip ratio, as expected, continued its rapid decline. The strip ratio averaged 1.3 tons of waste for every ton of ore in the March quarter, down from 3 -to -1 in the prior quarter. It's on track to reduce further in the June quarter and average at around 1 -to -1 in the current half year.
From mid-2023 onwards, we expect the average life of mine strip ratio to be around only 1.2- to -1 for the remaining three to four years of the mine life. The strip ratio is a key driver of cash operating costs at Koolan Island. Reductions to these levels, along with increasing ore shipments, are expected to see ongoing reductions in cash operating costs and significant growth in operating cash flows. Processing activities continue to be constrained while repairs to the damaged product screening area from the August 2022 fire incident were undertaken. The interim processing activities utilized the undamaged front crushing and screening sections of the main plant and were also supplemented by the commencement of a contract crushing contractor late during March.
Processed volumes were sufficient to maintain an average rate of three shipments per month across the quarter. As a result, nine shipments totaling 664,000 tons were completed in the quarter. Slightly better than forecast in our prior market update and included five shipments in March, which was a great result. This made up for wet season interruptions and delays to the processing plant repairs related to transport disruptions that we had earlier in the quarter from the Kimberley flooding events. That limited our sales to two shipments in each of the first two months of the quarter, January and February. The average shipped iron grade for the quarter was 65.3% Fe as planned and confirms Koolan Island as Australia's highest grade direct shipping iron ore operation.
This meant that sales for the nine-month year-to-date period totaled 1.78 million tons at an average grade of 65.1% Fe. Consistent with the decision that we made when the processing plant fire occurred in August last year, we continued to mine ore from the open pit in line with the mine plan and have assembled the substantial mined ore stockpiles available for processing as the crushing capacity ramps up. At period end, as I mentioned, these stocks totaled over 1.2 million tons. In relation to insurance, in re the August 2022 plant fire incident, Mount Gibson does maintain relevant property damage and business interruption insurance cover for the Koolan Island operations.
Up to the end of the quarter, progress payments from our insurers totaling AUD 2.7 million had been received and further interim claims are made and to be paid in due course. The improved operational results underpinned a significant turnaround in Koolan Island's underlying financial performance in the March quarter, as you can expect. Ore sales revenue totaled AUD 112 million FOB, reflecting an average realized price of $121 FOB, equivalent to around AUD 180 at the current exchange rate. This revenue is also inclusive of provisional pricing adjustments for various shipments arising from subsequent ore price increases.
These adjustments reflect the fact that most of Koolan's sales are contracted on a deferred N+1 or N+2 basis, where the price ultimately paid by our customer is based on the average of the first or second month after the shipment is made. Shipping freight rates for Panamax vessel journeys from Koolan Island to Northern China range from $11-$14 a ton in the March quarter, compared with $12-$16 per ton in the preceding quarter. Current shipping freight rates for the Panamax vessels that are used at Koolan Island are around $14 a ton shipped. At current prices, each high-grade shipment from Koolan Island has a market value of approximately AUD 12 million FOB before royalties.
Operating cash flow from Koolan Island totaled AUD 31 million for the quarter, a substantial turnaround from the outflow of AUD 3 million reported in the previous quarter. All sales revenues totaled AUD 112 million, as noted, and the key outflow items were cash operating costs of AUD 55 million, inventory build of AUD 14 million, royalties of AUD 11 million, and net crusher repair costs of AUD 1 million after insurance proceeds are taken into account. The operations unit cash operating costs were AUD 84 per tonne FOB in the quarter and before inventory build and royalties. These are expected to reduce in the June quarter so that we can achieve the annual target of around AUD 75 FOB before the inventory build and royalties for the year. We also expect these to reduce again in the coming 2023/2024 financial year.
In relation to the group's financial performance for the quarter, the group's cash flow totaled AUD 28 million, and that comprised the AUD 31 million operating cash flow from Koolan that I noted above, plus a net inflow from our Midwest operations of AUD 2 million after exploration costs of AUD 1 million and net corporate overhead costs of AUD 4 million. After positive working capital movements totaling AUD 14 million, and that included the receipt of the provisional pricing upward adjustments I mentioned earlier. The company's cash and investments balance increased to AUD 83 million at the end of the quarter, and that compares with AUD 41 million at the end of December last year. As a result of the performance, no further drawn down will be necessary on the company's existing AUD 100 million revolving credit facility. The existing drawn amount of AUD 25 million is expected to be repaid in full in the June quarter.
In relation to our Midwest business, cash flow includes the rail credit refund we received, which is accruing at a rate of about AUD 2 million per quarter. The total credit that we received is capped at a maximum of approximately AUD 35 million, subject to indexation. To date, we've received total cumulative proceeds of approximately AUD 32 million. We expect to receive the final payment later this year. We also continue to receive and consider external inquiries regarding our Midwest infrastructure assets, in particular, key rail sidings and port storage sheds, from where we already receive some income from third-party usage arrangements. Discussions remain in progress regarding further arrangements for the utilization of that capacity within those assets. Looking forward, in accordance with our recent guidance, we're targeting total high-grade ore sales of approximately 2.9 million tons in the current 2022/2023 financial year.
Unit cash operating costs are expected to reduce in the June quarter to achieve our annual target of around AUD 75 per tonne FOB for royalties and inventory build, as I mentioned, and then to reduce further in the coming financial year ahead. Wrapping up, the March quarter was a key positive inflection point for our business, as you can see, as the processing plant repairs were completed and shipping rates started to increase. Sales and cash flow are expected to build substantially in the June quarter. Based on the operations forecast, mining and shipping profile, including the extensive mined ore stockpiles that have been built in recent months, the business is well-positioned to achieve its targeted increases in sales and operating cash flows going forward. We look forward to reporting on that at the end of the June quarter.
With that, I'll hand back to you, Luke, for any questions that listeners may have.
Thank you, Peter. To our audience, joined us on the teleconference, your opportunity to ask a question is now by pressing star one on your telephone keypad. It's star one on your telephone keypad to queue for a question. We'll pause a moment to assemble a question queue. We don't appear to have any questions. I'll hand back over to Peter and the team for any further or closing remarks.
Okay. Thank you, Luke. We know that it's a busy morning, so appreciate everyone's time on the call. If you do have questions, please come back to John or myself on the usual numbers, and we'd be happy to help you. Have a good day. Thanks, Luke.
Thank you. That concludes today's Mount Gibson Iron March Quarter Activities teleconference. All participants may disconnect.