No gold and silver are found in Precolombian sites in Northeastern North America. So how does gold get there in the ATL?
Oh there are small gold deposits (not sure about silver) throughout eastern canada and up into the Canadian shield, as well as copper deposits (some which were used by natives, others which weren't). Plus bog iron - which they found and smelted at their way-station on the northern tip of New Found land. What it would take for these other metals to be found is luck and time and exploration.
The natives are going to stop Vinland expansion eventually.
Maybe yes, maybe no.
It depends. If "Vinland" can hold Newfoundland (aka part of Markland, but that's beside the point), P.E.I., a few other islands in the Gulf, and really "Norse-ize" them, they'll be well set. Population will explode (with the fisheries supplementing their agriculture/herds) and trade with flourish with the old world moreso then OTL. And with increased trade comes an increase in disease exchange with the old world.
Basically, what it comes down too is having Vinland reach a critical population mass where trade flourishes, and second, what diseases come and when. That Vinland will eventually be stopped is likely, but the difference is where it is stopped? In the Gulf, or in OTL Ontario, or the west coast.