Collectibility of trade receivables is reviewed on an ongoing basis at an operating unit level. Individual debts that are known to  be uncollectible are written off when identified. An impairment provision is recognised when there is objective evidence that the  Consolidated Entity will not be able to collect the receivable. Financial difficulties of the debtor, default payments or debts more than 60  days overdue are considered objective evidence of impairment. The amount of the impairment loss is the receivable carrying amount  compared to the present value of estimated future cash flows, discounted at the original effective interest rate. During the year due to an increase in the Tin metal price there was a reversal of inventory write-downs of $1,832,571 (2010:  reversal of write-down $2,967,314) for the Consolidated Entity. This expense is included in cost of sales refer to note 7(a). 88  NOTES TO THE CONSOLIDATED FINANCIAL STATEMENTS FOR THE YEAR ENDED 30 JUNE 2011 15. OTHER ASSETS (CURRENT) 16. OTHER FINANCIAL ASSETS (CURRENT) 17 AVAILABLE-FOR-SALE FINANCIAL ASSETS (NON-CURRENT) 14. INVENTORIES (CURRENT) 2011 2010 Ore stocks at net realisable value 147,395  823,380  Tin in circuit at cost 132,757  207,420  Tin concentrate at cost 10,747,418  11,806,514  Copper concentrate at cost 49,731  - Stores and spares at cost 2,460,701  2,229,166  Provision for obsolete stores and spares (369,042) (244,903) Total inventories at lower of cost and net realisable value 13,168,960  14,821,577  2011 2010 Prepayments 146,177  874,561  2011 2010 Other financial asset (a) 750,000  750,000  Other receivables - cash on deposit - performance bond facility (b) 2,570,730  4,255,260  3,320,730  5,005,260  2011 2010 Shares - Australian listed 47,004,755  34,064,803  Shares - British Virgin Island unlisted 2,000,000  - 49,004,755  34,064,803  (a) Other financial assets are used by way of security for the mining contractor at the Bluestone Mines Tasmania Joint Venture. (b) The cash on deposit is interest bearing and is used by way of security for government performance bonds. (a) Trade receivables are non-interest bearing and are generally on 30 - 90 day terms. (b) Other debtors primarily relate to cash calls advanced to the Bluestone Mines Tasmania Joint  Venture. Other debtors are non-interest bearing and are generally on 30 - 90 day terms. (c) The carrying amounts disclosed above represent the fair value.