"银行抵押业务" can be translated into English as "bank mortgage services" or "bank mortgage lending business".
"Bank mortgage services" is a more general term that encompasses all the services related to mortgages provided by a bank, including loan origination, processing, underwriting, and servicing.
"Bank mortgage lending business" specifically refers to the business activity of a bank in providing mortgage loans to borrowers.
Both translations are accurate and commonly used, depending on the context and the specific aspect of the mortgage business you want to emphasize.