Spurned by Rio Tinto RIO.AU +0.86% PLC, Glencore GLNCY -2.40% PLC CEO Ivan Glasenberg continued to look at other potential iron ore targets with a call to U.S. minerCliffs Natural Resources Inc., CLF -0.95% according to people familiar with the matter.

Glencore talked to Cliffs about its Australian iron ore assets around a month ago, these people said. While that conversation was described as very preliminary, the call underscores that Mr. Glasenberg isn't placing all his iron ore ambitions on another attempt at Rio Tinto.

Earlier this week, Rio Tinto said Glencore had approached it in July about a possible takeover, which would have created the world’s biggest mining company by value.

Glencore isn’t a major producer of iron ore but has a large marketing arm that trades the product for other miners. Buying up active miners, or combining with Rio Tinto, would allow it to trade its own product, and potentially to bolster prices by closing mines or delaying expansion.

The Swiss-based commodities giant, whose portfolio ranges from cotton to zinc and grains, is prohibited under U.K. takeover rules from making a new approach on Rio Tinto for at least six months. But as Mr. Glasenberg weighs whether to make a second attempt on London-listed Rio, he still retains an open mind on other iron-ore assets, according to two London-based bankers.

In August, Cleveland-based Cliffs hired banks to sell some U.S. coal assets along with its Australian iron ore mines as it looks to focus on five core U.S. iron ore mines.

Two people familiar with the matter said that there have been no firm offers on Cliffs’ Australian mines, which are based in the west of the country, though several companies and Chinese steelmakers have expressed preliminary interest. The state of the iron ore market could lead the company to shelve its current efforts to sell these mines, one of these people said.

A 40% fall in the price of iron ore has made such sales more difficult as buyers wait for the market to calm and sellers become reluctant to sell at lower prices. Iron ore, a key ingredient in steelmaking, has fallen amid worries about a supply glut that could take years to clear.

Mr. Glasenberg, an active deal maker who often casts his net wide when looking at potential targets, has shopped for iron ore assets before. Last year, Glencore circled Rio Tinto’s Canadian iron ore operations before backing away, people familiar with the matter said at the time. Rio Tinto didn’t end up selling its 59% stake in the Canadian mine. Before this summer, Glencore also looked at Guinea’s Simandou iron-ore mine.