A 50 per cent share price gain in three months has prompted analyst downgrades for Oz Minerals, as the miner is finalising development plans for a new project and amid optimism over its exploration profile. Argonaut Securities has a "sell" recommendation on the miner's shares and Morgans, along with Morningstar, "reduce" calls. "We think that Oz Mineral's recent +50 per cent re-rating has been driven by generalist demand for large, liquid, high margin copper exposures amid rising copper prices and new exuberance for global growth," Morgans analyst Tom Sartor told clients. "Such exposures are scarce on the ASX, helping to explain the premium. "However, with prices now well ahead of fundamentals, we think the market is overlooking Oz Mineral's inherent risks." Morningstar has a $4 a share valuation, arguing simply that "Oz Minerals is overvalued". "The company an the market are likely too bullish on the outlook for copper as China's demand falls," it told clients Tuesday. Management's forecast of a long term copper price of $US3 a pound, which is well above the spot price of $US2.20 a pound is "overly optimistic" it told clients. The shares eased Monday to close at $9.08, down 8¢ from Friday's close, but well ahead of levels of below $6 in late October last year. Specifically, the concerns relate to the development of the proposed Carrapateena mine at a large copper deposit in South Australia, and the associated treatment plant, given the complex orebody. Oz Minerals on Monday reported a large rise in cash on hand to $656 million, up $103 million over the past year as it benefited from high metal prices, particularly the recent run up in the price of copper. Revenue in 2016 hit an estimated $820 million, it said. The buoyant copper price means it expects to begin paying tax so that from 2017 dividends will be franked, it told analysts. At Carrapateena, project feasibility is being studied with a decision likely by around mid-year, with tenders already under way for some long lead time equipment. If the go ahead is given, this project is to be in operation by 2020. A focus is the suite of exploration projects being advanced, aimed at underwriting the group's growth prospects. Here, most attention is on the remote Wet Musgrave prospect west of the corner of the border of South Australia and the Northern Territory, where Oz Mineral is farming into acreage held by junior explorer Cassini Resources. Oz Minerals is to spend up to $36 million to earn a 70 per cent interest in this prospect with near-term studies on metallurgy and potential commercialisation given the remote location. Upwards of 40 kilometres of mineralised strike length has been confirmed at West Musgrave, although exploration to date is limited. "We are in a new district and will likely see other resources defined," the chief executive, Andrew Cole, told analysts. "There is a lot of exploration upside to come," Hartley's analyst Mike Millikan said of the prospects for West Musgrave, with the potential of the acreage underscored by Oz Minerals decision to commit funds to assessing the prospect.