A brand new article
from Jonas Scherner forecloses the notion that Germany could rapidly have been defeated by shutting off access to certain metals.
I won't hold this against the OP, as such notions underlay much of Allied strategy and there were serious proposals
to rely on it even more heavily. Scherner's article also uncovers much German blockade preparation that was intentionally concealed from the public and even from in the German government.
On tungsten, for example:
In the case of tungsten, the exploration programme continued after the start of the war.164 In 1942, the Reichsamt für Bodenforschung considered the German tungsten mines as rich as those of Portugal and Spain.165 By the end of 1942, when annual German production amounted to only 180 tons per annum, standby capacities would have allowed an immediate annual output increase to 700 tons per annum, roughly one-third of German tungsten consumption in 1943.166 Yet, up to mid-1944, a full utilisation of these standby capacities was not considered necessary. Only when it was certain that tungsten imports from the Iberian Peninsula, so far the main foreign source, would stop in the second half of 1944, was a massive capacity expansion of the German tungsten mines ordered. Within a year, total German tungsten production was supposed to increase to 1,200 tons, covering two-thirds of Germany’s consumption needs.167 Combined with the still-existing stocks, German tungsten consumption could have been met up to 1948.168
The basic error in historical strategy and in nearly all subsequent historiography is to neglect the possibility of substitution in matters of both demand and supply. Mark Harrison has a good treatment
of the economic/theoretical framework.
As Harrison reminds us, substitution is not costless. To replace Iberian tungsten, for example, Germany would have had to re-task workers into their standby mining capacity. Scherner's article doesn't discuss iron ore but even taking Narvik would only have forced Germany to produce more domestically and in occupied Europe (Salzgitter, Alsace, later the SU).Of course the cost of substitution for some materials - oil most prominently - can be enormous.
Nonetheless, imposing substitution costs on Germany would have come nowhere close to the disastrous economic results predicted by people like Churchill when he pushed his various peripheral and mineral-focused schemes. These schemes almost certainly would have cost more to the Allied war effort than the substitution costs imposed on Germany.