Most of the metal necklaces sold by are costume jewelry, and so the important feature to note is not the composition but the color of the metal:

Gold-Tone Metal:
Jacob Olesen tells us that, "Gold indicates winning, success, achievement and triumph and is associated with abundance, prosperity, well-being, affluence, extravagance, prestige and elegance. Gold is uplifting and positive, infused with optimism, enlightenment and heightened spirituality.
"Gold represents masculinity and is the color of the sun, reflecting generosity, happiness, tradition and brilliance. []

Silver-Tone Metal:
Jacob Olesen tells us that, "Silver is associated with the moon and the tides and is considered to be feminine energy, cleansing, illuminating and showing the way forward and connected to the higher self, spirituality, creativity and introspection.
"Silver is symbolic of wealth and truth, technology and craftsmanship, and brings both moon magic and removes negativity. It is sleek and modern and invokes high-tech, precision, and strength." []

Black-Tone Metal:
Kate Smith tells us that, "Black is authoritative, powerful and mysterious, evoking potential and possibility, and providing a restful emptiness. It is associated with sophistication and power, symbolizes the combination of all colors of the universe and, as represented by a Black Belt, is the beginning of true achievement, understanding and wisdom, with the bending of the mind and body into one, and into a unity within oneself and with the universe." []

Pewter-Tone Metal: tells us that, "Pewter retains the gray characteristics of neutrality and seriousness, and its darker hue conveys a certain weightiness. As a neutral color, it plays well with every color in the spectrum. But when using pewter in design, balance its depth with a lighter color, such as creams and light grays for the best effect."

High quality metals: tells us: "Like stones, metals also possess magical qualities.  Gold, silver, and copper are the most common metals used in jewelry and other mystical objects.  Gold has a powerful but somewhat aloof aura, with a solar/masculine tone; this metal suggests purity, wealth, virtue, and permanence.  It grants protection and longevity.  This very soft, easily worked metal was among the first that humans learned how to use.  It appears on many magical and sacred items in historic and modern times.  For mystical purposes, peridot yields the greatest strength when set in gold.  Ancient alchemists used to seek ways of turning base metals, like lead, into gold.

"Silver has an equally powerful but more accessible aura, with a lunar/feminine tone; this metal suggests fluidity, intuition, and transformation.  It is also the metal most receptive to magical imprints or programming – like psychic SillyPutty.  To keep silver from picking up too much “junk” energy, you can loop a bit of silver wire around a quartz crystal and store that in the case with your silver jewelry.  This will soak up impressions and keep the other silver magically clean.  It’s easier to take out the wrapped quartz and purify it once a month, than to be stuck cleaning your whole silver collection.

"Copper, a lively conductor of electricity, has a feminine aura.  It works well for balancing the body’s energies, attracting love, bringing luck, or maintaining health.  Copper is sacred to Venus.  Sometimes it’s used for an athame blade or a wand, because it directs energy so well.  The best place to wear copper is on the side opposite your dominant hand; copper bracelets are a good choice and easy to find.

"Other metals occasionally show up in jewelry too.  Brass and bronze sometimes substitute for gold, magically speaking; they convey protection and carry a similar solar/masculine tone.  While similar to silver in its ability to hold a magical charge, platinum is a bit more assertive, which makes it less inclined to pick up random impressions.  Iron sometimes appears in novelties made of horseshoe nails or in the form of meteorites, both of which have strong magical associations of their own; this metal conveys splendid protection and also works well for binding, dispelling, or grounding purposes.

"Ideally, the setting of magical jewelry should have an opening in the back or bottom to allow skin contact with the gem.  Too much base metal in the setting can make it less suitable for magical work by diluting the energy.  The style should also evoke the desired goal – perhaps a dragon to grant courage or a regular knotwork pattern to balance energy flows.  The setting may also reflect the body part in need of attention, like feet for speed, to employ the sympathetic magic of similarity.  Traditional symbols such as pentacles, trefoils, stars, and spirals are ideal setting motifs for a Pagan’s stone that will be used for many different purposes."