Glencore to cut spending, take $790 mln writedown on Chad oil assets

* Expects full-year capex at $6 bln from $6.5-$6.8 bln

* First (Other OTC: FSTC - news) -half copper output down 3 pct (Rewrites throughout, adds analyst comment)

By Olivia Kumwenda-Mtambo

JOHANNESBURG, Aug 13 (Reuters) - Miner and commodity trader Glencore (Xetra: A1JAGV - news) on Thursday cut back its spending plans for this year and said it would take a $790 million charge on oil assets in Chad after a fall in oil prices.

The London-listed company, due to report half-year results next week, said its capital expenditure ceiling for 2015 was expected to be $6 billion, down from a range of $6.5-$6.8 billion announced in February.

Glencore's action on spending follows sharp falls across commodity prices this year, partly on the back of a slowdown in China, which is one of the world's biggest consumers of metals and other raw materials.

The 19-commodity Thomson Reuters/Core Commodity CRB Index , for example, is currently at a 12-year low.

Other big mining groups have reined in spending plans and begun cutting costs. Rio Tinto (LSE: RIO.L - news) this month said it planned $1 billion in cost cuts this year and Anglo American (LSE: AAL.L - news) is to cut thousands of jobs in the next few years and may sell assets.

Glencore bought Chad-focused oil company Caracal Energy for about 800 million pounds ($1.25 billion) last year, a deal that allowed the commodity group to move upstream in the oil sector.

The company said it had made "significant amendments" to the Chad operation's work programme following a sharp decline in oil prices, including changes to the fields' capital expenditure and production profiles. Oil prices are down because of a supply glut.

The company said it expected to take the $790 million impairment charge on the value of the operations in its interim accounts.

"We expect the company to unveil further capex reductions in 2016-17 at the results next Wednesday, underlining the commitment to its credit rating and dividends," Barclays (Swiss: BARC.SW - news) analysts said in a note.

In Glencore's 2014 results in March, the company said net debt fell by $5.3 billion to $30.5 billion.

Glencore said its first-half copper output using feed from its own sources fell 3 percent to 730,900 tonnes and full-year output would be between 1.5 million tonnes and 1.55 million tonnes.

Copper is the largest earner for the company.

Production of coal, another major commodity for Glencore, fell 4 percent decline to 68.7 million tonnes, mainly due to reduction in Australian thermal output.

Coal prices have also been weak and as a result Glencore (Amsterdam: GX8.AS - news) plans to shut part of its Optimum Coal mine in South Africa. It has also begun a "business rescue" for the mine as it tries to renegotiate a supply contract with South African power utility Eskom. Glencore says Eskom was paying too little for its coal.

"The directors of Optimum are of the view that if the supply agreement with Eskom can be renegotiated, there is a reasonable prospect of rescuing Optimum," the company said in a statement.

Glencore shares fell to record lows on Wednesday and are down around 40 percent since the beginning of the year, under pressure from the rout in the commodity prices. They were 0.5 percent up by 0927 GMT on Thursday. ($1 = 0.6405 pounds) (Editing by James Macharia and Jane Merriman)