I have a Whites 5900 Di Pro SL and it works well in highly mineralized soil (manual ground balance is very handy), but not for small gold. The 4900 and 5900 are similar in a lot of ways, so I doubt yours will find much gold directly with it (1 gram or larger nuggets are easy to find with one if its not too deep, but those are not that common).
I also have a Whites Goldmaster/Vsat (circa 1994) and GMT. Both work extremely well for small gold (with the smaller 4X6 DD coil being very sensitive - the smaller coil size is good for looking up along the river bench areas - the standard coil is too large to work around the irregular shaped river rock I work). I wish the GMT could detach the controls from the shaft of the detector, like the GM/VSat can - it makes for much less stress on the arm over time. I bought my GM2 and GM/VSat units off of eBay and I find that with a DD coil they work just as well as a GMT (you just have learn how to ground balance them - find I mostly run my GMT in manual GB mode, but I like its ground grab facility to set a start point at).
I have found that my 5900 works pretty well for finding Silver ore (depending on ore chemistry). Your 4900 might work ok for that if you can learn to ground balance it - I recall that the 4900 was sold as a prospecting detector (along with coin hunting) 30 years ago. Also, keep in mind that its 6.8 Khz (just like the 5900 and 6000), which is not a good frequency for prospecting small gold. 12 Khz and above work a lot better for finding gold.
Practice with your 4900 and give it a try. You never know what you find if you don't get out there and look. It will find concentrations of deposited black sand - that does not necessarily mean gold, but it might point to places where gold might have collected. Fine (100+ mesh) gold is in many rivers that come out of Colorado (traveling as far as Nebraska and Kansas) - there are few detectors that will find flakes as small as 30+ mesh gold, so sometimes, if you know its potentially there, you look for black sand and sample with a pan.