CHICAGO, June 12 (Reuters) - Basis bids for soybeans delivered by barge to U.S. Gulf Coast terminals were steady to lower on Thursday, and corn bids ticked lower, traders said.

• Chicago Board of Trade soybean futures Sv1 fell to one-week lows on Thursday as collapsing domestic cash markets, poor weekly export sales and worries about the size of U.S. biofuel mandates raised fears about demand for the oilseed, brokers said.

• The slump, particularly in the spot July SN25 contract, reflected weakening cash markets after several domestic soy processors sharply lowered their bids to buy old-crop soybeans.

• Poor weekly export sales added pressure.

• Spot soybean basis bids were down at U.S. Midwest processors and mostly down at river terminals on Thursday, according to a spot check. Archer-Daniels-Midland Co locations were dropping their bids as they rolled over the November contract for soybeans, and other facilities followed suit.

• The U.S. Environmental Protection Agency on Friday will propose new biofuel blending requirements for oil refiners for the coming two years that will likely include a lower biomass-based diesel mandate than industry groups had requested, according to four sources familiar with the matter.

• In monthly supply-demand reports, the U.S. Department of Agriculture left its forecasts of U.S. old- and new-crop soybean inventories unchanged from last month, as analysts expected.

• CIF soybean barges loaded in June were bid at 66 cents over Chicago Board of Trade July SN25 futures, steady from Wednesday.

• July soybean barge loadings traded at 74 cents over July futures for a second day, market sources said.

• FOB export premiums for soybeans loaded from the Gulf in June were offered at about 78 cents over July futures, down 2 cents.

• For corn, CIF barges loaded in June were bid at 66 cents over CBOT July corn futures CN25, down 1 cent.

• FOB export premiums for corn shipped from the Gulf in June were offered at about 81 cents over CBOT July corn futures, down 1 cent.

(Reporting By P.J. Huffstutter; Editing by Alan Barona)

((pj.huffstutter@thomsonreuters.com; 313-484-5275 (w)))

For displays of CIF basis, click on the codes in brackets:
U.S. CIF Gulf soybeans GRYM
U.S. CIF Gulf corn GRYN
U.S. CIF Gulf SRW wheat GRYO
U.S. CIF Gulf HRW wheat GRYP
For displays of FOB basis, please click on the following codes in brackets:
U.S. FOB Gulf corn GRZC
U.S. FOB Gulf soybeans GRZD
U.S. FOB Gulf SRW wheat GRZE
U.S. FOB Gulf HRW wheat GRZF

LINKS Corn prices page:   cpurl://apps.cp./cms/?pageid=corn-cash-market
Wheat prices page:  cpurl://apps.cp./cms/?pageid=wheat-cash-market
U.S. barge freight                  BG/US
U.S. export sales estimates         USDA/EST
U.S. grain export summary           GRA/U
Brazil soybean export prices        SYBS
Brazil corn export prices           SYBX
Argentina grain prices              GRA/ARG
Russia grain prices                 GRA/RU