Hello, and welcome to today's Petra Diamonds third quarter trading update. My name is Bailey, and I will be the moderator for today's call. All lines will be muted during the presentation portion of the call, with an opportunity for questions and answers at the end. If you would like to ask a question, please press star followed by one on your telephone keypad. I would now like to pass the conference over to Richard Duffy, CEO. Please go ahead.
Good morning and good afternoon, everybody, and thank you for joining us today for a discussion of our third quarter and nine-month trading update for this financial year, 2022. I'm joined today by Jacques Breytenbach, our CFO. After Jacques and I have taken you through our trading update, we'll hand back to the operator to take your questions. Please also note that we are recording the call, which is available on our website. As ever, safety first. We are very pleased to have continued our strong downward trend on injuries. Our lost time injury frequency rate decreased 62% to 0.18 from 0.47 this time last year. In an absolute sense, lost time injuries decreased 20% from 30 to 24, and were of low severity and mostly behavioral in nature.
This improvement is a measure of the success of our remedial actions and behavior-based intervention programs. COVID-19 remains a risk which we continue to manage with minimal disruption to operations. The focus on vaccinations continues, making them readily available and encouraging their uptake. In South Africa, 2,479 employees have been fully vaccinated, which is 58% of our workforce, with another 244 partially vaccinated. At the half year, 53% of the workforce was fully vaccinated. At Williamson, the vaccination campaign is progressing, although the rollout has been slower, with 14% vaccinated. Turning to our revenue in the diamond market, our Q3 revenue at $140.6 million rose 33% with year-to-date revenue of $405.4 million, up 43% as compared to the corresponding period in financial year 2021.
This was driven in particular by exceptional stone sales of $83.4 million. It is worth noting that notwithstanding the significant contribution from exceptionals, we continue to use Cullinan's five-year average of $37 million annually for our planning purposes. The other driver was the very strong results of the fourth tender, where like-for-like prices increased by just under 38% versus our tender three in December of last year. While we expect continued strong demand for rough diamonds, supported by the structural change in supply and demand, we do not expect these to continue at the same level seen in our fourth tender. This follows the uncertainty around the impact of the Ukraine war on the global economy in particular, and caution around the potential effect of the renewed COVID lockdown in China.
Having said that, we continue to see a supportive diamond market, which has been evident since mid-2021. On the demand side, the strength is driven by strong jewelry sales and increased demand from the manufacturing centers, trends which have continued since the run-up to the festive season in December last year. On the supply side, as mentioned, the structural deficit between supply and demand is set to continue. Petra is closely monitoring the impact of the war in Ukraine and sanctions on Russian companies. While it is not clear exactly how these sanctions are affecting supply, we do expect some level of disruption. As I'm sure you're aware, at Petra we follow the Kimberley Process and are able to prove provenance of all of our diamonds.
COVID-19 has had little or no impact on the attendance at our tenders in this financial year, but we will continue our flexible approach in planning upcoming sales to cater for any disruption. The fifth sales results will be announced around the end of April, and our final sale for this financial year, 2022, is planned towards the end of June. The year-to-date 16% reduction in carats sold, which was 31% down in the third quarter versus the same period last year, is the result of higher sales volumes at the start of financial year 2021, following inventory buildup in financial year 2020 after the initial COVID-19 outbreak. While sales in this quarter three were limited to only one tender as opposed to the usual two.
The higher diamond inventory at the end of quarter three is expected to unwind to normal year-end levels by the end of this financial year. Turning to production. Our production for the nine months at just over 2.6 million carats was up 7% and 18% higher in quarter three, in line with our guidance. This reflects the resumption of production at Williamson in the first half of this financial year, 2022, versus the corresponding period in financial year 2021 when the mine was still in care and maintenance. Quarterly comparator was affected by the remedial steps taken at Finsch to deal with the waste ingress in financial year 2021 versus the much stronger operational performance by the mine in this quarter three.
The waste ingress at Finsch, which I've just referred to, has been largely mitigated through the implementation of enhanced drill and blast and draw controls to curtail the level of waste in the mine. Remediation of tunnel 41 at Cullinan is complete following the convergence in that area as previously reported, and we continue to monitor the area in terms of re-accessing the tunnel again. Our annual production guidance of 1.7-1.9 million carats at Cullinan and 1.3-1.4 million carats at Finsch remains unchanged. As announced in the interims, the business reengineering projects at Finsch and Koffiefontein have been concluded and are now being implemented. At Finsch, this means cost savings and production improvement initiatives targeting enhanced margins to ensure a long-term sustainable operation. These are now factored into our annual three-year plan.
At Koffiefontein, we have confirmed running the mine to closure in 2025 while simultaneously exploring other options. We are engaging with the Future Forum, which comprises organized labor and management, to align the operations to reduce tonnage profile and improve efficiencies. As you know, Project 2022 is a three-year project that ends in June of this year. This project has delivered improved cash generation through increased production and reduced operating and capital spend. Improved operating performance has been particularly evident at Cullinan and Finsch since Project 2022's inception.
We have delivered net free cash flow across the business of $182 million for the 30 months to 31 December 2021, and are confident that we will deliver over $200 million for the full 36-month period by the end of June this year, thereby exceeding our Project 2022 $100 million-$150 million target by some margin. Importantly, business improvement is now embedded in our operating model and is an integral part of our operating culture. Turning to Williamson mine, I will now provide a brief update on the progress we've made there with regard to remedial steps taken in response to the historical allegations of human rights abuses. Progress continues to be made in establishing the independent grievance mechanism and community projects.
The government of Tanzania has given its support to proceed with local stakeholder engagement on the independent grievance mechanism in early February, and the first phase of this engagement commenced in March. Further engagement is required before launching the independent grievance mechanism, which is now expected in the last quarter of this calendar year. The medical services project providing support to local communities is up and running, and feasibility studies for the income-producing agribusiness and artisanal mining projects are progressing. I will now hand over to Jacques to provide us with an overview of our financial position. Jacques.
Richard, good morning or afternoon to everyone on the call. I will briefly touch on our balance sheet, which has strengthened further during the period. We are delighted to see net debt closing the third quarter at $107 million, down from $152 million at the end of December. We ended the quarter with gross cash balances of $249 million and unrestricted cash balances of $233 million. Importantly, these balances are stated after settling our first lien facilities during the three-month period, which totaled some $88.9 million, including interest until the date of settlement.
The agreements of the new ZAR 1 billion or $68 million revolving credit facility with Absa Bank, which we announced in February, are in the process of being finalized, with the new facility expected to become effective towards the end of April. We did not have any diamond debtor receivable at the end of the quarter, compared to some $400,000 receivable at the end of December. At March 31, the group's diamond inventory was valued at $98.1 million, up from just under $80 million in December. This is largely attributable to the timing of our tenders, with inventory expected to unwind with two further tenders planned in quarter four, as also mentioned by Richard. Finally, we are delighted to also confirm that the credit rating agencies have upgraded Petra during the quarter.
Moody's upgraded our corporate and secondary bond rating from Caa1 to B3 in recognition of our stronger financial and business outlook, to use their words. They also improved the outlook from positive to stable. S&P have also upgraded its outlook for Petra's bonds to positive while maintaining the B- rating, improved liquidity. I'll hand back to Richard.
In conclusion, let me say that although we do anticipate some pullback in diamond prices from the elevated March tender levels, the structural shift in the diamond market continues to buoy the industry. This, coupled with our operational improvements resulting from Project 2022, driving margin and cash generation, supports a positive outlook for Petra, with potential for further reductions in our debt levels going forward. That concludes our overview of the trading update, and we would like to invite your questions, which will be managed by the operator. Thank you.
Thank you. If you would like to ask a question, please press star followed by one on your telephone keypad. If for any reason you would like to remove that question, please press star followed by two. Again, to ask a question, it is star followed by one. As a reminder, if you are using a speaker phone, please remember to pick up your handset before asking your question. We will pause here briefly as questions are registered. As a reminder, if you would like to ask a question, it is star followed by one on your telephone keypad. It appears there are no questions waiting at this time, so I'd like to pass the call back over to Richard Duffy. Please go ahead.
Thanks very much, Bailey. There being no questions, I'd just like to thank all of you, all of you for your participation, and we look forward to talking to you again in the near future. Thanks very much.
Thank you, everyone.
That concludes today's Petra Diamonds third quarter trading update. Thank you for your participation. You may now disconnect your line.