With mortgage origination volume dropping sharply and gain-on-sale margins shrinking, it’s not surprising that the biggest downturn in mortgage-banking income during the third quarter came from production-related activities rather than servicing. A new Inside Mortgage Trends analysis of earnings shows that 10 major lenders reported a total of $1.66 billion in production-related income during the third quarter of 2013. That was down a whopping 62.5 percent from the second quarter. Total mortgage [Includes one data chart]