(ShareCast News) - Recovering from an initial lurch lower, the FTSE 250 index scrambled higher over the course of Monday's session, helped by optimism in some mining investors.Serco was top riser among London's mid-caps, however, as the outsourcing group was boosted by RBC Capital Markets upgrading the stock to 'sector perform' from 'underperform'. "Whilst risks clearly remain and the recovery will take time, for the first time in a while we see more limited downside and the balance sheet is no longer an issue post the Intelenet disposal," the bank said.Miner Petra Diamonds was lifted as investors re-examined its production report last week, with broker Canaccord Genuity also reiterating a buy recommendation and a target price of 150p, almost double the current price. Analysts warned of three potential headwinds to share price growth: further weakness in the diamond market from inventory building, Petra surprisingly maintaining its own price guidance from July levels, and Petra's lack of clarity over conversations with its banks about debt.Shares in Ophir Energy were up despite weak Chinese data published over the weekend and the company revealing that it had plugged and abandoned an exploration well as its Soy Siam prospect in Thailand, having found all reservoirs were dry and no hydrocarbon shows were encountered. The drill rig will now move to Ophir's Parichat South West prospect which is independent of Soy Siam as it is testing a different petroleum system.IP Group was lifted 1.6% after one of its portfolio companies, Ultrahaptics Limited, has completed a fundraising for £10.1m. Based on current valuation, IPG's undiluted beneficial direct stake and via its IP Venture Fund II enjoyed an unrealised fair value gain to IP Group of £4.6m and a fair value gain of £1.6m to IP Venture Fund II.Among the fallers, Pets at Home continued to be dogged by poor sentiment in the weekend press after it admitted on Friday that trading in parts of the business had been weaker than expected.Gold miner Acacia Mining was weighed down by a fall in prices of the yellow metal. FTSE 250 - RisersSerco Group (SRP) 99.75p 6.46%Petra Diamonds Ltd.(DI) (PDL) 79.20p 6.10%Ophir Energy (OPHR) 101.00p 5.26%Premier Oil (PMO) 71.55p 4.45%Kaz Minerals (KAZ) 121.20p 4.39%National Express Group (NEX) 311.60p 4.07%International Personal Finance (IPF) 383.10p 3.51%Just Eat (JE.) 440.10p 3.31%Indivior (INDV) 212.30p 3.26%Shawbrook Group (SHAW) 350.00p 3.15%FTSE 250 - FallersAcacia Mining (ACA) 183.60p -4.87%Pets at Home Group (PETS) 275.40p -4.54%esure Group (ESUR) 258.90p -2.30%Petrofac Ltd. (PFC) 826.00p -2.02%Henderson Group (HGG) 282.10p -1.74%SIG (SHI) 131.30p -1.65%Derwent London (DLN) 3,820.00p -1.55%Hansteen Holdings (HSTN) 122.20p -1.53%Tullow Oil (TLW) 199.90p -1.48%Supergroup (SGP) 1,442.00p -1.37%